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 $84.74   9.285%   $92.6081   $92.61   $92.60   $92.60  
  Purchase #2 $148.56   7.767%   $160.0987   $160.10   $160.10   $160.10  
  Purchase #3 $16.42   7.427%   $17.6395   $17.64   $17.65   $17.60  
  Purchase #4 $145.57   9.554%   $159.4778   $159.48   $159.50   $159.50  
  Purchase #5 $247.69   4.748%   $259.4503   $259.45   $259.45   $259.50  
  Purchase #6 $19.60   4.838%   $20.5482   $20.55   $20.55   $20.50  
  Purchase #7 $119.58   4.727%   $125.2325   $125.23   $125.25   $125.20  
  7 purchase totals = $782.16       $835.0551   $835.06   $835.10   $835.00