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 $144.71   11.784%   $161.7626   $161.76   $161.75   $161.80  
  Purchase #2 $88.64   6.848%   $94.7101   $94.71   $94.70   $94.70  
  Purchase #3 $50.29   4.639%   $52.623   $52.62   $52.60   $52.60  
  Purchase #4 $93.77   9.318%   $102.5075   $102.51   $102.50   $102.50  
  Purchase #5 $229.81   6.323%   $244.3409   $244.34   $244.35   $244.30  
  Purchase #6 $171.91   10.823%   $190.5158   $190.52   $190.50   $190.50  
  Purchase #7 $120.50   11.754%   $134.6636   $134.66   $134.65   $134.70  
  7 purchase totals = $899.63       $981.1235   $981.12   $981.05   $981.10