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 $152.79   6.713%   $163.0468   $163.05   $163.05   $163.00  
  Purchase #2 $59.94   9.521%   $65.6469   $65.65   $65.65   $65.60  
  Purchase #3 $54.57   10.222%   $60.1481   $60.15   $60.15   $60.10  
  Purchase #4 $91.99   8.585%   $99.8873   $99.89   $99.90   $99.90  
  Purchase #5 $201.25   4.333%   $209.9702   $209.97   $209.95   $210.00  
  Purchase #6 $12.52   11.696%   $13.9843   $13.98   $14.00   $14.00  
  Purchase #7 $239.84   13.227%   $271.5636   $271.56   $271.55   $271.60  
  7 purchase totals = $812.90       $884.2472   $884.25   $884.25   $884.20