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 $237.71   12.664%   $267.8136   $267.81   $267.80   $267.80  
  Purchase #2 $247.87   8.363%   $268.5994   $268.60   $268.60   $268.60  
  Purchase #3 $24.92   10.813%   $27.6146   $27.61   $27.60   $27.60  
  Purchase #4 $95.59   9.165%   $104.3508   $104.35   $104.35   $104.40  
  Purchase #5 $116.65   12.618%   $131.3689   $131.37   $131.35   $131.40  
  Purchase #6 $45.31   12.568%   $51.0046   $51.00   $51.00   $51.00  
  Purchase #7 $146.27   9.580%   $160.2827   $160.28   $160.30   $160.30  
  7 purchase totals = $914.32       $1,011.0346   $1,011.02   $1,011.00   $1,011.10