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 $225.62   11.844%   $252.3424   $252.34   $252.35   $252.30  
  Purchase #2 $81.38   5.145%   $85.567   $85.57   $85.55   $85.60  
  Purchase #3 $36.66   13.302%   $41.5365   $41.54   $41.55   $41.50  
  Purchase #4 $143.80   9.194%   $157.021   $157.02   $157.00   $157.00  
  Purchase #5 $110.31   13.712%   $125.4357   $125.44   $125.45   $125.40  
  Purchase #6 $54.66   13.472%   $62.0238   $62.02   $62.00   $62.00  
  Purchase #7 $240.97   12.120%   $270.1756   $270.18   $270.20   $270.20  
  7 purchase totals = $893.40       $994.1020   $994.11   $994.10   $994.00