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 $69.87   6.645%   $74.5129   $74.51   $74.50   $74.50  
  Purchase #2 $74.86   11.675%   $83.5999   $83.60   $83.60   $83.60  
  Purchase #3 $59.84   11.323%   $66.6157   $66.62   $66.60   $66.60  
  Purchase #4 $246.42   10.301%   $271.8037   $271.80   $271.80   $271.80  
  Purchase #5 $203.51   11.566%   $227.048   $227.05   $227.05   $227.00  
  Purchase #6 $48.95   12.487%   $55.0624   $55.06   $55.05   $55.10  
  Purchase #7 $212.89   13.659%   $241.9686   $241.97   $241.95   $242.00  
  7 purchase totals = $916.34       $1,020.6112   $1,020.61   $1,020.55   $1,020.60