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 $224.94   12.752%   $253.6243   $253.62   $253.60   $253.60  
  Purchase #2 $181.68   4.756%   $190.3207   $190.32   $190.30   $190.30  
  Purchase #3 $170.51   4.852%   $178.7831   $178.78   $178.80   $178.80  
  Purchase #4 $155.54   9.657%   $170.5605   $170.56   $170.55   $170.60  
  Purchase #5 $178.99   5.774%   $189.3249   $189.32   $189.30   $189.30  
  Purchase #6 $58.93   10.246%   $64.968   $64.97   $64.95   $65.00  
  Purchase #7 $108.81   13.303%   $123.285   $123.29   $123.30   $123.30  
  7 purchase totals = $1,079.40       $1,170.8665   $1,170.86   $1,170.80   $1,170.90