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 $58.59   7.535%   $63.0048   $63.00   $63.00   $63.00  
  Purchase #2 $135.73   3.774%   $140.8525   $140.85   $140.85   $140.90  
  Purchase #3 $52.98   11.838%   $59.2518   $59.25   $59.25   $59.30  
  Purchase #4 $175.37   10.371%   $193.5576   $193.56   $193.55   $193.60  
  Purchase #5 $84.86   4.797%   $88.9307   $88.93   $88.95   $88.90  
  Purchase #6 $249.68   9.755%   $274.0363   $274.04   $274.05   $274.00  
  Purchase #7 $187.91   5.816%   $198.8388   $198.84   $198.85   $198.80  
  7 purchase totals = $945.12       $1,018.4725   $1,018.47   $1,018.50   $1,018.50