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 $152.72   6.746%   $163.0225   $163.02   $163.00   $163.00  
  Purchase #2 $247.86   9.539%   $271.5034   $271.50   $271.50   $271.50  
  Purchase #3 $68.97   7.325%   $74.0221   $74.02   $74.00   $74.00  
  Purchase #4 $246.39   5.174%   $259.1382   $259.14   $259.15   $259.10  
  Purchase #5 $206.29   8.788%   $224.4188   $224.42   $224.40   $224.40  
  Purchase #6 $119.43   11.314%   $132.9423   $132.94   $132.95   $132.90  
  Purchase #7 $99.83   7.464%   $107.2813   $107.28   $107.30   $107.30  
  7 purchase totals = $1,141.49       $1,232.3286   $1,232.32   $1,232.30   $1,232.20