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 $103.68   11.483%   $115.5856   $115.59   $115.60   $115.60  
  Purchase #2 $55.82   12.189%   $62.6239   $62.62   $62.60   $62.60  
  Purchase #3 $37.95   9.335%   $41.4926   $41.49   $41.50   $41.50  
  Purchase #4 $223.38   11.771%   $249.6741   $249.67   $249.65   $249.70  
  Purchase #5 $234.40   10.285%   $258.508   $258.51   $258.50   $258.50  
  Purchase #6 $132.65   13.523%   $150.5883   $150.59   $150.60   $150.60  
  Purchase #7 $206.29   10.466%   $227.8803   $227.88   $227.90   $227.90  
  7 purchase totals = $994.17       $1,106.3528   $1,106.35   $1,106.35   $1,106.40