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 $234.99   13.766%   $267.3387   $267.34   $267.35   $267.30  
  Purchase #2 $230.69   3.309%   $238.3235   $238.32   $238.30   $238.30  
  Purchase #3 $161.95   9.607%   $177.5085   $177.51   $177.50   $177.50  
  Purchase #4 $220.82   6.706%   $235.6282   $235.63   $235.65   $235.60  
  Purchase #5 $96.60   6.665%   $103.0384   $103.04   $103.05   $103.00  
  Purchase #6 $50.48   5.367%   $53.1893   $53.19   $53.20   $53.20  
  Purchase #7 $7.46   11.385%   $8.3093   $8.31   $8.30   $8.30  
  7 purchase totals = $1,002.99       $1,083.3359   $1,083.34   $1,083.35   $1,083.20