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 $168.33   9.495%   $184.3129   $184.31   $184.30   $184.30  
  Purchase #2 $230.38   10.561%   $254.7104   $254.71   $254.70   $254.70  
  Purchase #3 $146.49   7.535%   $157.528   $157.53   $157.55   $157.50  
  Purchase #4 $237.80   11.696%   $265.6131   $265.61   $265.60   $265.60  
  Purchase #5 $220.46   11.342%   $245.4646   $245.46   $245.45   $245.50  
  Purchase #6 $110.72   9.406%   $121.1343   $121.13   $121.15   $121.10  
  Purchase #7 $87.44   7.276%   $93.8021   $93.80   $93.80   $93.80  
  7 purchase totals = $1,201.62       $1,322.5654   $1,322.55   $1,322.55   $1,322.50