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 $84.68   10.618%   $93.6713   $93.67   $93.65   $93.70  
  Purchase #2 $134.29   9.192%   $146.6339   $146.63   $146.65   $146.60  
  Purchase #3 $245.48   12.266%   $275.5906   $275.59   $275.60   $275.60  
  Purchase #4 $136.41   12.602%   $153.6004   $153.60   $153.60   $153.60  
  Purchase #5 $145.79   12.274%   $163.6843   $163.68   $163.70   $163.70  
  Purchase #6 $87.62   8.302%   $94.8942   $94.89   $94.90   $94.90  
  Purchase #7 $246.70   13.685%   $280.4609   $280.46   $280.45   $280.50  
  7 purchase totals = $1,080.97       $1,208.5356   $1,208.52   $1,208.55   $1,208.60