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 $199.81   6.103%   $212.0044   $212.00   $212.00   $212.00  
  Purchase #2 $233.98   6.631%   $249.4952   $249.50   $249.50   $249.50  
  Purchase #3 $69.45   8.799%   $75.5609   $75.56   $75.55   $75.60  
  Purchase #4 $134.85   9.111%   $147.1362   $147.14   $147.15   $147.10  
  Purchase #5 $129.39   11.729%   $144.5662   $144.57   $144.55   $144.60  
  Purchase #6 $57.91   12.146%   $64.9437   $64.94   $64.95   $64.90  
  Purchase #7 $213.43   3.354%   $220.5884   $220.59   $220.60   $220.60  
  7 purchase totals = $1,038.82       $1,114.2950   $1,114.30   $1,114.30   $1,114.30