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 $60.92   13.777%   $69.3129   $69.31   $69.30   $69.30  
  Purchase #2 $238.98   6.273%   $253.9712   $253.97   $253.95   $254.00  
  Purchase #3 $248.82   11.648%   $277.8026   $277.80   $277.80   $277.80  
  Purchase #4 $92.64   9.855%   $101.7697   $101.77   $101.75   $101.80  
  Purchase #5 $9.51   11.506%   $10.6042   $10.60   $10.60   $10.60  
  Purchase #6 $49.76   11.227%   $55.3466   $55.35   $55.35   $55.30  
  Purchase #7 $72.44   13.185%   $81.9912   $81.99   $82.00   $82.00  
  7 purchase totals = $773.07       $850.7984   $850.79   $850.75   $850.80