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 $48.27   5.106%   $50.7347   $50.73   $50.75   $50.70  
  Purchase #2 $198.41   13.384%   $224.9652   $224.97   $224.95   $225.00  
  Purchase #3 $230.36   3.703%   $238.8902   $238.89   $238.90   $238.90  
  Purchase #4 $60.26   6.356%   $64.0901   $64.09   $64.10   $64.10  
  Purchase #5 $206.72   7.764%   $222.7697   $222.77   $222.75   $222.80  
  Purchase #6 $89.88   11.210%   $99.9555   $99.96   $99.95   $100.00  
  Purchase #7 $41.86   6.400%   $44.539   $44.54   $44.55   $44.50  
  7 purchase totals = $875.76       $945.9444   $945.95   $945.95   $946.00