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 $39.29   12.184%   $44.0771   $44.08   $44.10   $44.10  
  Purchase #2 $148.73   3.403%   $153.7913   $153.79   $153.80   $153.80  
  Purchase #3 $121.80   9.565%   $133.4502   $133.45   $133.45   $133.50  
  Purchase #4 $181.79   13.785%   $206.8498   $206.85   $206.85   $206.80  
  Purchase #5 $134.32   13.220%   $152.0771   $152.08   $152.10   $152.10  
  Purchase #6 $245.84   9.667%   $269.6054   $269.61   $269.60   $269.60  
  Purchase #7 $47.63   9.104%   $51.9662   $51.97   $51.95   $52.00  
  7 purchase totals = $919.40       $1,011.8171   $1,011.83   $1,011.85   $1,011.90