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 $238.54   10.562%   $263.7346   $263.73   $263.75   $263.70  
  Purchase #2 $44.56   3.735%   $46.2243   $46.22   $46.20   $46.20  
  Purchase #3 $79.28   4.458%   $82.8143   $82.81   $82.80   $82.80  
  Purchase #4 $162.40   7.779%   $175.0331   $175.03   $175.05   $175.00  
  Purchase #5 $152.29   5.698%   $160.9675   $160.97   $160.95   $161.00  
  Purchase #6 $77.82   11.463%   $86.7405   $86.74   $86.75   $86.70  
  Purchase #7 $17.58   9.805%   $19.3037   $19.30   $19.30   $19.30  
  7 purchase totals = $772.47       $834.8180   $834.80   $834.80   $834.70