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 $243.96   6.298%   $259.3246   $259.32   $259.30   $259.30  
  Purchase #2 $202.93   11.547%   $226.3623   $226.36   $226.35   $226.40  
  Purchase #3 $158.33   9.305%   $173.0626   $173.06   $173.05   $173.10  
  Purchase #4 $72.39   8.106%   $78.2579   $78.26   $78.25   $78.30  
  Purchase #5 $87.26   9.306%   $95.3804   $95.38   $95.40   $95.40  
  Purchase #6 $190.79   6.637%   $203.4527   $203.45   $203.45   $203.50  
  Purchase #7 $82.33   7.340%   $88.373   $88.37   $88.35   $88.40  
  7 purchase totals = $1,037.99       $1,124.2135   $1,124.20   $1,124.15   $1,124.40