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 $44.56   13.508%   $50.5792   $50.58   $50.60   $50.60  
  Purchase #2 $246.64   9.633%   $270.3988   $270.40   $270.40   $270.40  
  Purchase #3 $78.28   4.216%   $81.5803   $81.58   $81.60   $81.60  
  Purchase #4 $43.48   11.590%   $48.5193   $48.52   $48.50   $48.50  
  Purchase #5 $200.64   13.185%   $227.0944   $227.09   $227.10   $227.10  
  Purchase #6 $228.85   6.474%   $243.6657   $243.67   $243.65   $243.70  
  Purchase #7 $227.52   8.689%   $247.2892   $247.29   $247.30   $247.30  
  7 purchase totals = $1,069.97       $1,169.1269   $1,169.13   $1,169.15   $1,169.20