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 $54.33   13.232%   $61.5189   $61.52   $61.50   $61.50  
  Purchase #2 $123.43   9.585%   $135.2608   $135.26   $135.25   $135.30  
  Purchase #3 $89.61   13.763%   $101.943   $101.94   $101.95   $101.90  
  Purchase #4 $173.26   8.852%   $188.597   $188.60   $188.60   $188.60  
  Purchase #5 $104.61   6.482%   $111.3908   $111.39   $111.40   $111.40  
  Purchase #6 $64.27   11.167%   $71.447   $71.45   $71.45   $71.40  
  Purchase #7 $27.51   12.395%   $30.9199   $30.92   $30.90   $30.90  
  7 purchase totals = $637.02       $701.0774   $701.08   $701.05   $701.00