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 $55.62   10.194%   $61.2899   $61.29   $61.30   $61.30  
  Purchase #2 $242.62   8.242%   $262.6167   $262.62   $262.60   $262.60  
  Purchase #3 $216.25   11.349%   $240.7922   $240.79   $240.80   $240.80  
  Purchase #4 $112.72   12.184%   $126.4538   $126.45   $126.45   $126.50  
  Purchase #5 $147.46   12.813%   $166.354   $166.35   $166.35   $166.40  
  Purchase #6 $15.60   8.532%   $16.931   $16.93   $16.95   $16.90  
  Purchase #7 $84.65   11.194%   $94.1257   $94.13   $94.15   $94.10  
  7 purchase totals = $874.92       $968.5633   $968.56   $968.60   $968.60