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   5.316%   $59.9564   $59.96   $59.95   $60.00  
  Purchase #2 $219.31   8.513%   $237.9799   $237.98   $238.00   $238.00  
  Purchase #3 $129.58   4.398%   $135.2789   $135.28   $135.30   $135.30  
  Purchase #4 $177.70   3.731%   $184.33   $184.33   $184.35   $184.30  
  Purchase #5 $98.93   9.554%   $108.3818   $108.38   $108.40   $108.40  
  Purchase #6 $101.79   3.120%   $104.9658   $104.97   $104.95   $105.00  
  Purchase #7 $250.42   7.547%   $269.3192   $269.32   $269.30   $269.30  
  7 purchase totals = $1,034.66       $1,100.2120   $1,100.22   $1,100.25   $1,100.30