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 $244.44   12.869%   $275.897   $275.90   $275.90   $275.90  
  Purchase #2 $157.31   13.193%   $178.0639   $178.06   $178.05   $178.10  
  Purchase #3 $98.67   6.125%   $104.7135   $104.71   $104.70   $104.70  
  Purchase #4 $218.52   6.224%   $232.1207   $232.12   $232.10   $232.10  
  Purchase #5 $103.91   6.261%   $110.4158   $110.42   $110.40   $110.40  
  Purchase #6 $41.63   7.266%   $44.6548   $44.65   $44.65   $44.70  
  Purchase #7 $192.80   11.127%   $214.2529   $214.25   $214.25   $214.30  
  7 purchase totals = $1,057.28       $1,160.1186   $1,160.11   $1,160.05   $1,160.20