Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $191.87   9.457%   $210.0151   $210.02   $210.00   $210.00  
  Purchase #2 $212.31   13.336%   $240.6237   $240.62   $240.60   $240.60  
  Purchase #3 $169.37   10.823%   $187.7009   $187.70   $187.70   $187.70  
  Purchase #4 $186.34   11.320%   $207.4337   $207.43   $207.45   $207.40  
  Purchase #5 $216.87   8.353%   $234.9852   $234.99   $235.00   $235.00  
  Purchase #6 $113.60   9.729%   $124.6521   $124.65   $124.65   $124.70  
  Purchase #7 $223.86   7.565%   $240.795   $240.80   $240.80   $240.80  
  7 purchase totals = $1,314.22       $1,446.2057   $1,446.21   $1,446.20   $1,446.20