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 $232.48   6.814%   $248.3212   $248.32   $248.30   $248.30  
  Purchase #2 $177.50   12.462%   $199.6201   $199.62   $199.60   $199.60  
  Purchase #3 $200.54   6.110%   $212.793   $212.79   $212.80   $212.80  
  Purchase #4 $131.38   8.726%   $142.8442   $142.84   $142.85   $142.80  
  Purchase #5 $49.75   10.382%   $54.915   $54.92   $54.90   $54.90  
  Purchase #6 $99.40   3.203%   $102.5838   $102.58   $102.60   $102.60  
  Purchase #7 $70.25   4.670%   $73.5307   $73.53   $73.55   $73.50  
  7 purchase totals = $961.30       $1,034.6080   $1,034.60   $1,034.60   $1,034.50