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 $32.32   7.471%   $34.7346   $34.73   $34.75   $34.70  
  Purchase #2 $53.81   10.389%   $59.4003   $59.40   $59.40   $59.40  
  Purchase #3 $69.43   5.201%   $73.0411   $73.04   $73.05   $73.00  
  Purchase #4 $204.61   4.530%   $213.8788   $213.88   $213.90   $213.90  
  Purchase #5 $215.99   9.107%   $235.6602   $235.66   $235.65   $235.70  
  Purchase #6 $169.78   12.236%   $190.5543   $190.55   $190.55   $190.60  
  Purchase #7 $227.68   6.675%   $242.8776   $242.88   $242.90   $242.90  
  7 purchase totals = $973.62       $1,050.1469   $1,050.14   $1,050.20   $1,050.20