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 $53.26   13.751%   $60.5838   $60.58   $60.60   $60.60  
  Purchase #2 $36.52   8.427%   $39.5975   $39.60   $39.60   $39.60  
  Purchase #3 $65.27   9.546%   $71.5007   $71.50   $71.50   $71.50  
  Purchase #4 $110.77   11.285%   $123.2704   $123.27   $123.25   $123.30  
  Purchase #5 $205.99   9.244%   $225.0317   $225.03   $225.05   $225.00  
  Purchase #6 $186.96   6.190%   $198.5328   $198.53   $198.55   $198.50  
  Purchase #7 $32.79   4.616%   $34.3036   $34.30   $34.30   $34.30  
  7 purchase totals = $691.56       $752.8205   $752.81   $752.85   $752.80