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 $114.58   8.394%   $124.1978   $124.20   $124.20   $124.20  
  Purchase #2 $215.97   9.367%   $236.1999   $236.20   $236.20   $236.20  
  Purchase #3 $227.88   7.798%   $245.6501   $245.65   $245.65   $245.70  
  Purchase #4 $110.93   9.641%   $121.6248   $121.62   $121.60   $121.60  
  Purchase #5 $244.35   6.637%   $260.5675   $260.57   $260.55   $260.60  
  Purchase #6 $85.81   11.123%   $95.3546   $95.35   $95.35   $95.40  
  Purchase #7 $13.49   5.363%   $14.2135   $14.21   $14.20   $14.20  
  7 purchase totals = $1,013.01       $1,097.8082   $1,097.80   $1,097.75   $1,097.90