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 $56.93   12.154%   $63.8493   $63.85   $63.85   $63.80  
  Purchase #2 $70.72   11.184%   $78.6293   $78.63   $78.65   $78.60  
  Purchase #3 $61.78   4.201%   $64.3754   $64.38   $64.40   $64.40  
  Purchase #4 $52.69   6.257%   $55.9868   $55.99   $56.00   $56.00  
  Purchase #5 $87.55   7.326%   $93.9639   $93.96   $93.95   $94.00  
  Purchase #6 $143.93   8.590%   $156.2936   $156.29   $156.30   $156.30  
  Purchase #7 $26.75   6.606%   $28.5171   $28.52   $28.50   $28.50  
  7 purchase totals = $500.35       $541.6154   $541.62   $541.65   $541.60