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 $71.52   10.813%   $79.2535   $79.25   $79.25   $79.30  
  Purchase #2 $110.51   10.842%   $122.4915   $122.49   $122.50   $122.50  
  Purchase #3 $96.71   13.405%   $109.674   $109.67   $109.65   $109.70  
  Purchase #4 $210.62   9.409%   $230.4372   $230.44   $230.45   $230.40  
  Purchase #5 $13.98   11.193%   $15.5448   $15.54   $15.55   $15.50  
  Purchase #6 $94.85   6.695%   $101.2002   $101.20   $101.20   $101.20  
  Purchase #7 $90.25   13.654%   $102.5727   $102.57   $102.55   $102.60  
  7 purchase totals = $688.44       $761.1739   $761.16   $761.15   $761.20