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 $63.25   3.814%   $65.6624   $65.66   $65.65   $65.70  
  Purchase #2 $24.85   12.534%   $27.9647   $27.96   $27.95   $28.00  
  Purchase #3 $84.49   10.758%   $93.5794   $93.58   $93.60   $93.60  
  Purchase #4 $224.47   9.727%   $246.3042   $246.30   $246.30   $246.30  
  Purchase #5 $171.45   11.768%   $191.6262   $191.63   $191.65   $191.60  
  Purchase #6 $231.41   9.800%   $254.0882   $254.09   $254.10   $254.10  
  Purchase #7 $45.51   3.472%   $47.0901   $47.09   $47.10   $47.10  
  7 purchase totals = $845.43       $926.3152   $926.31   $926.35   $926.40