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 $207.47   12.118%   $232.6112   $232.61   $232.60   $232.60  
  Purchase #2 $124.59   12.127%   $139.699   $139.70   $139.70   $139.70  
  Purchase #3 $56.87   13.108%   $64.3245   $64.32   $64.30   $64.30  
  Purchase #4 $81.27   7.322%   $87.2206   $87.22   $87.20   $87.20  
  Purchase #5 $224.62   12.770%   $253.304   $253.30   $253.30   $253.30  
  Purchase #6 $73.50   5.599%   $77.6153   $77.62   $77.60   $77.60  
  Purchase #7 $164.50   4.489%   $171.8844   $171.88   $171.90   $171.90  
  7 purchase totals = $932.82       $1,026.6590   $1,026.65   $1,026.60   $1,026.60