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 $120.70   4.856%   $126.5612   $126.56   $126.55   $126.60  
  Purchase #2 $244.65   8.138%   $264.5596   $264.56   $264.55   $264.60  
  Purchase #3 $204.33   12.459%   $229.7875   $229.79   $229.80   $229.80  
  Purchase #4 $86.39   10.268%   $95.2605   $95.26   $95.25   $95.30  
  Purchase #5 $238.37   6.280%   $253.3396   $253.34   $253.35   $253.30  
  Purchase #6 $27.69   5.705%   $29.2697   $29.27   $29.25   $29.30  
  Purchase #7 $247.76   6.238%   $263.2153   $263.22   $263.20   $263.20  
  7 purchase totals = $1,169.89       $1,261.9934   $1,262.00   $1,261.95   $1,262.10