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 $162.87   12.366%   $183.0105   $183.01   $183.00   $183.00  
  Purchase #2 $96.56   8.121%   $104.4016   $104.40   $104.40   $104.40  
  Purchase #3 $32.80   7.332%   $35.2049   $35.20   $35.20   $35.20  
  Purchase #4 $63.62   3.246%   $65.6851   $65.69   $65.70   $65.70  
  Purchase #5 $211.40   5.829%   $223.7225   $223.72   $223.70   $223.70  
  Purchase #6 $108.65   3.122%   $112.0421   $112.04   $112.05   $112.00  
  Purchase #7 $102.75   7.700%   $110.6618   $110.66   $110.65   $110.70  
  7 purchase totals = $778.65       $834.7285   $834.72   $834.70   $834.70