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 $93.47   10.459%   $103.246   $103.25   $103.25   $103.20  
  Purchase #2 $21.71   9.480%   $23.7681   $23.77   $23.75   $23.80  
  Purchase #3 $85.68   3.728%   $88.8742   $88.87   $88.85   $88.90  
  Purchase #4 $108.65   7.378%   $116.6662   $116.67   $116.65   $116.70  
  Purchase #5 $128.86   12.538%   $145.0165   $145.02   $145.00   $145.00  
  Purchase #6 $195.97   4.767%   $205.3119   $205.31   $205.30   $205.30  
  Purchase #7 $61.35   6.649%   $65.4292   $65.43   $65.45   $65.40  
  7 purchase totals = $695.69       $748.3121   $748.32   $748.25   $748.30