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 $235.28   8.184%   $254.5353   $254.54   $254.55   $254.50  
  Purchase #2 $97.85   7.346%   $105.0381   $105.04   $105.05   $105.00  
  Purchase #3 $14.48   12.633%   $16.3093   $16.31   $16.30   $16.30  
  Purchase #4 $67.35   10.479%   $74.4076   $74.41   $74.40   $74.40  
  Purchase #5 $114.35   7.659%   $123.1081   $123.11   $123.10   $123.10  
  Purchase #6 $168.42   7.160%   $180.4789   $180.48   $180.50   $180.50  
  Purchase #7 $29.84   11.832%   $33.3707   $33.37   $33.35   $33.40  
  7 purchase totals = $727.57       $787.2480   $787.26   $787.25   $787.20