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 $84.82   9.610%   $92.9712   $92.97   $92.95   $93.00  
  Purchase #2 $249.37   6.561%   $265.7312   $265.73   $265.75   $265.70  
  Purchase #3 $159.98   12.807%   $180.4686   $180.47   $180.45   $180.50  
  Purchase #4 $78.69   3.221%   $81.2246   $81.22   $81.20   $81.20  
  Purchase #5 $174.27   11.107%   $193.6262   $193.63   $193.65   $193.60  
  Purchase #6 $218.95   4.628%   $229.083   $229.08   $229.10   $229.10  
  Purchase #7 $93.29   3.704%   $96.7455   $96.75   $96.75   $96.70  
  7 purchase totals = $1,059.37       $1,139.8503   $1,139.85   $1,139.85   $1,139.80