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 $215.71   11.652%   $240.8445   $240.84   $240.85   $240.80  
  Purchase #2 $151.38   6.501%   $161.2212   $161.22   $161.20   $161.20  
  Purchase #3 $80.26   7.403%   $86.2016   $86.20   $86.20   $86.20  
  Purchase #4 $29.73   5.473%   $31.3571   $31.36   $31.35   $31.40  
  Purchase #5 $22.94   11.263%   $25.5237   $25.52   $25.50   $25.50  
  Purchase #6 $34.52   6.251%   $36.6778   $36.68   $36.70   $36.70  
  Purchase #7 $160.49   11.662%   $179.2063   $179.21   $179.20   $179.20  
  7 purchase totals = $695.03       $761.0322   $761.03   $761.00   $761.00