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 $62.29   7.483%   $66.9512   $66.95   $66.95   $67.00  
  Purchase #2 $182.69   12.166%   $204.9161   $204.92   $204.90   $204.90  
  Purchase #3 $126.54   13.459%   $143.571   $143.57   $143.55   $143.60  
  Purchase #4 $228.70   9.413%   $250.2275   $250.23   $250.25   $250.20  
  Purchase #5 $246.82   11.543%   $275.3104   $275.31   $275.30   $275.30  
  Purchase #6 $98.66   5.153%   $103.7439   $103.74   $103.75   $103.70  
  Purchase #7 $224.33   13.463%   $254.5315   $254.53   $254.55   $254.50  
  7 purchase totals = $1,170.03       $1,299.2516   $1,299.25   $1,299.25   $1,299.20