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 $84.57   3.562%   $87.5824   $87.58   $87.60   $87.60  
  Purchase #2 $32.84   8.534%   $35.6426   $35.64   $35.65   $35.60  
  Purchase #3 $76.99   3.230%   $79.4768   $79.48   $79.50   $79.50  
  Purchase #4 $15.52   6.633%   $16.5494   $16.55   $16.55   $16.50  
  Purchase #5 $105.43   4.389%   $110.0573   $110.06   $110.05   $110.10  
  Purchase #6 $204.27   6.662%   $217.8785   $217.88   $217.90   $217.90  
  Purchase #7 $215.39   11.486%   $240.1297   $240.13   $240.15   $240.10  
  7 purchase totals = $735.01       $787.3167   $787.32   $787.40   $787.30