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 $71.76   3.511%   $74.2795   $74.28   $74.30   $74.30  
  Purchase #2 $189.37   5.377%   $199.5524   $199.55   $199.55   $199.60  
  Purchase #3 $40.48   7.266%   $43.4213   $43.42   $43.40   $43.40  
  Purchase #4 $233.41   6.192%   $247.8627   $247.86   $247.85   $247.90  
  Purchase #5 $170.91   9.433%   $187.0319   $187.03   $187.05   $187.00  
  Purchase #6 $227.58   12.479%   $255.9797   $255.98   $256.00   $256.00  
  Purchase #7 $7.95   6.392%   $8.4582   $8.46   $8.45   $8.50  
  7 purchase totals = $941.46       $1,016.5857   $1,016.58   $1,016.60   $1,016.70