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 $226.32   11.679%   $252.7519   $252.75   $252.75   $252.80  
  Purchase #2 $224.45   3.834%   $233.0554   $233.06   $233.05   $233.10  
  Purchase #3 $132.65   13.667%   $150.7793   $150.78   $150.80   $150.80  
  Purchase #4 $43.68   8.261%   $47.2884   $47.29   $47.30   $47.30  
  Purchase #5 $112.88   12.774%   $127.2993   $127.30   $127.30   $127.30  
  Purchase #6 $228.79   12.862%   $258.217   $258.22   $258.20   $258.20  
  Purchase #7 $205.93   13.208%   $233.1292   $233.13   $233.15   $233.10  
  7 purchase totals = $1,174.70       $1,302.5205   $1,302.53   $1,302.55   $1,302.60