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 $38.96   12.725%   $43.9177   $43.92   $43.90   $43.90  
  Purchase #2 $152.61   13.629%   $173.4092   $173.41   $173.40   $173.40  
  Purchase #3 $37.79   10.252%   $41.6642   $41.66   $41.65   $41.70  
  Purchase #4 $54.98   10.593%   $60.804   $60.80   $60.80   $60.80  
  Purchase #5 $195.75   6.236%   $207.957   $207.96   $207.95   $208.00  
  Purchase #6 $206.73   6.676%   $220.5313   $220.53   $220.55   $220.50  
  Purchase #7 $236.29   13.570%   $268.3546   $268.35   $268.35   $268.40  
  7 purchase totals = $923.11       $1,016.6380   $1,016.63   $1,016.60   $1,016.70