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 $42.31   5.364%   $44.5795   $44.58   $44.60   $44.60  
  Purchase #2 $208.73   11.485%   $232.7026   $232.70   $232.70   $232.70  
  Purchase #3 $140.70   4.701%   $147.3143   $147.31   $147.30   $147.30  
  Purchase #4 $250.75   10.475%   $277.0161   $277.02   $277.00   $277.00  
  Purchase #5 $123.86   12.734%   $139.6323   $139.63   $139.65   $139.60  
  Purchase #6 $236.57   7.804%   $255.0319   $255.03   $255.05   $255.00  
  Purchase #7 $127.84   3.862%   $132.7772   $132.78   $132.80   $132.80  
  7 purchase totals = $1,130.76       $1,229.0539   $1,229.05   $1,229.10   $1,229.00