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 $138.29   9.621%   $151.5949   $151.59   $151.60   $151.60  
  Purchase #2 $149.42   7.641%   $160.8372   $160.84   $160.85   $160.80  
  Purchase #3 $146.65   13.811%   $166.9038   $166.90   $166.90   $166.90  
  Purchase #4 $160.66   10.480%   $177.4972   $177.50   $177.50   $177.50  
  Purchase #5 $212.99   11.373%   $237.2134   $237.21   $237.20   $237.20  
  Purchase #6 $69.72   8.555%   $75.6845   $75.68   $75.70   $75.70  
  Purchase #7 $53.48   3.289%   $55.239   $55.24   $55.25   $55.20  
  7 purchase totals = $931.21       $1,024.9700   $1,024.96   $1,025.00   $1,024.90