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 $207.67   13.519%   $235.7449   $235.74   $235.75   $235.70  
  Purchase #2 $238.62   13.685%   $271.2751   $271.28   $271.30   $271.30  
  Purchase #3 $58.49   5.847%   $61.9099   $61.91   $61.90   $61.90  
  Purchase #4 $76.60   10.114%   $84.3473   $84.35   $84.35   $84.30  
  Purchase #5 $189.33   8.707%   $205.815   $205.82   $205.80   $205.80  
  Purchase #6 $54.30   5.207%   $57.1274   $57.13   $57.15   $57.10  
  Purchase #7 $144.94   11.554%   $161.6864   $161.69   $161.70   $161.70  
  7 purchase totals = $969.95       $1,077.9060   $1,077.92   $1,077.95   $1,077.80