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 $83.88   13.116%   $94.8817   $94.88   $94.90   $94.90  
  Purchase #2 $82.80   7.269%   $88.8187   $88.82   $88.80   $88.80  
  Purchase #3 $106.31   5.852%   $112.5313   $112.53   $112.55   $112.50  
  Purchase #4 $136.45   7.513%   $146.7015   $146.70   $146.70   $146.70  
  Purchase #5 $186.35   7.871%   $201.0176   $201.02   $201.00   $201.00  
  Purchase #6 $43.74   8.153%   $47.3061   $47.31   $47.30   $47.30  
  Purchase #7 $202.44   8.594%   $219.8377   $219.84   $219.85   $219.80  
  7 purchase totals = $841.97       $911.0946   $911.10   $911.10   $911.00