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 $204.95   11.669%   $228.8656   $228.87   $228.85   $228.90  
  Purchase #2 $80.57   3.803%   $83.6341   $83.63   $83.65   $83.60  
  Purchase #3 $76.56   4.794%   $80.2303   $80.23   $80.25   $80.20  
  Purchase #4 $76.71   3.359%   $79.2867   $79.29   $79.30   $79.30  
  Purchase #5 $165.77   4.471%   $173.1816   $173.18   $173.20   $173.20  
  Purchase #6 $21.35   5.780%   $22.584   $22.58   $22.60   $22.60  
  Purchase #7 $87.46   4.551%   $91.4403   $91.44   $91.45   $91.40  
  7 purchase totals = $713.37       $759.2226   $759.22   $759.30   $759.20