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 $219.33   12.259%   $246.2177   $246.22   $246.20   $246.20  
  Purchase #2 $165.47   5.866%   $175.1765   $175.18   $175.20   $175.20  
  Purchase #3 $88.43   6.347%   $94.0427   $94.04   $94.05   $94.00  
  Purchase #4 $114.81   12.800%   $129.5057   $129.51   $129.50   $129.50  
  Purchase #5 $165.51   6.123%   $175.6442   $175.64   $175.65   $175.60  
  Purchase #6 $57.32   6.189%   $60.8675   $60.87   $60.85   $60.90  
  Purchase #7 $249.31   6.232%   $264.847   $264.85   $264.85   $264.80  
  7 purchase totals = $1,060.18       $1,146.3013   $1,146.31   $1,146.30   $1,146.20