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 $23.90   10.115%   $26.3175   $26.32   $26.30   $26.30  
  Purchase #2 $241.46   6.144%   $256.2953   $256.30   $256.30   $256.30  
  Purchase #3 $85.85   11.484%   $95.709   $95.71   $95.70   $95.70  
  Purchase #4 $95.65   12.744%   $107.8396   $107.84   $107.85   $107.80  
  Purchase #5 $49.67   10.422%   $54.8466   $54.85   $54.85   $54.80  
  Purchase #6 $145.81   9.508%   $159.6736   $159.67   $159.65   $159.70  
  Purchase #7 $55.39   5.303%   $58.3273   $58.33   $58.35   $58.30  
  7 purchase totals = $697.73       $759.0089   $759.02   $759.00   $758.90