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 $248.86   5.658%   $262.9405   $262.94   $262.95   $262.90  
  Purchase #2 $19.95   3.527%   $20.6536   $20.65   $20.65   $20.70  
  Purchase #3 $132.49   9.443%   $145.001   $145.00   $145.00   $145.00  
  Purchase #4 $87.66   4.869%   $91.9282   $91.93   $91.95   $91.90  
  Purchase #5 $25.95   8.753%   $28.2214   $28.22   $28.20   $28.20  
  Purchase #6 $59.36   4.489%   $62.0247   $62.02   $62.00   $62.00  
  Purchase #7 $223.80   12.322%   $251.3766   $251.38   $251.40   $251.40  
  7 purchase totals = $798.07       $862.1460   $862.14   $862.15   $862.10