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 $224.96   8.470%   $244.0141   $244.01   $244.00   $244.00  
  Purchase #2 $96.78   5.565%   $102.1658   $102.17   $102.15   $102.20  
  Purchase #3 $111.64   5.475%   $117.7523   $117.75   $117.75   $117.80  
  Purchase #4 $80.87   5.432%   $85.2629   $85.26   $85.25   $85.30  
  Purchase #5 $245.93   7.765%   $265.0265   $265.03   $265.05   $265.00  
  Purchase #6 $47.85   7.488%   $51.433   $51.43   $51.45   $51.40  
  Purchase #7 $137.47   11.634%   $153.4633   $153.46   $153.45   $153.50  
  7 purchase totals = $945.50       $1,019.1179   $1,019.11   $1,019.10   $1,019.20