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 $55.34   11.224%   $61.5514   $61.55   $61.55   $61.60  
  Purchase #2 $209.42   7.186%   $224.4689   $224.47   $224.45   $224.50  
  Purchase #3 $103.98   12.343%   $116.8143   $116.81   $116.80   $116.80  
  Purchase #4 $88.79   10.731%   $98.3181   $98.32   $98.30   $98.30  
  Purchase #5 $156.94   13.830%   $178.6448   $178.64   $178.65   $178.60  
  Purchase #6 $249.83   12.481%   $281.0113   $281.01   $281.00   $281.00  
  Purchase #7 $17.57   12.816%   $19.8218   $19.82   $19.80   $19.80  
  7 purchase totals = $881.87       $980.6306   $980.62   $980.55   $980.60