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 $49.51   13.267%   $56.0785   $56.08   $56.10   $56.10  
  Purchase #2 $52.34   11.640%   $58.4324   $58.43   $58.45   $58.40  
  Purchase #3 $52.80   13.490%   $59.9227   $59.92   $59.90   $59.90  
  Purchase #4 $83.58   11.681%   $93.343   $93.34   $93.35   $93.30  
  Purchase #5 $191.68   12.458%   $215.5595   $215.56   $215.55   $215.60  
  Purchase #6 $175.83   10.858%   $194.9216   $194.92   $194.90   $194.90  
  Purchase #7 $226.63   11.864%   $253.5174   $253.52   $253.50   $253.50  
  7 purchase totals = $832.37       $931.7751   $931.77   $931.75   $931.70