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 $58.57   11.566%   $65.3442   $65.34   $65.35   $65.30  
  Purchase #2 $99.56   8.809%   $108.3302   $108.33   $108.35   $108.30  
  Purchase #3 $141.71   11.425%   $157.9004   $157.90   $157.90   $157.90  
  Purchase #4 $78.52   4.441%   $82.0071   $82.01   $82.00   $82.00  
  Purchase #5 $243.79   3.355%   $251.9692   $251.97   $251.95   $252.00  
  Purchase #6 $218.99   10.646%   $242.3037   $242.30   $242.30   $242.30  
  Purchase #7 $239.80   9.740%   $263.1565   $263.16   $263.15   $263.20  
  7 purchase totals = $1,080.94       $1,171.0113   $1,171.01   $1,171.00   $1,171.00