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 $197.27   13.657%   $224.2112   $224.21   $224.20   $224.20  
  Purchase #2 $121.77   12.149%   $136.5638   $136.56   $136.55   $136.60  
  Purchase #3 $108.52   10.131%   $119.5142   $119.51   $119.50   $119.50  
  Purchase #4 $77.96   8.654%   $84.7067   $84.71   $84.70   $84.70  
  Purchase #5 $245.36   12.613%   $276.3073   $276.31   $276.30   $276.30  
  Purchase #6 $243.81   3.684%   $252.792   $252.79   $252.80   $252.80  
  Purchase #7 $207.58   13.669%   $235.9541   $235.95   $235.95   $236.00  
  7 purchase totals = $1,202.27       $1,330.0493   $1,330.04   $1,330.00   $1,330.10