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 $91.52   4.649%   $95.7748   $95.77   $95.75   $95.80  
  Purchase #2 $139.78   9.549%   $153.1276   $153.13   $153.15   $153.10  
  Purchase #3 $52.94   12.594%   $59.6073   $59.61   $59.60   $59.60  
  Purchase #4 $98.64   8.478%   $107.0027   $107.00   $107.00   $107.00  
  Purchase #5 $8.58   10.582%   $9.4879   $9.49   $9.50   $9.50  
  Purchase #6 $217.68   12.663%   $245.2448   $245.24   $245.25   $245.20  
  Purchase #7 $241.82   4.759%   $253.3282   $253.33   $253.35   $253.30  
  7 purchase totals = $850.96       $923.5733   $923.57   $923.60   $923.50