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 $47.60   11.222%   $52.9417   $52.94   $52.95   $52.90  
  Purchase #2 $247.64   9.566%   $271.3292   $271.33   $271.35   $271.30  
  Purchase #3 $53.92   5.840%   $57.0689   $57.07   $57.05   $57.10  
  Purchase #4 $240.73   7.795%   $259.4949   $259.49   $259.50   $259.50  
  Purchase #5 $70.83   6.337%   $75.3185   $75.32   $75.30   $75.30  
  Purchase #6 $198.69   10.534%   $219.62   $219.62   $219.60   $219.60  
  Purchase #7 $182.59   9.565%   $200.0547   $200.05   $200.05   $200.10  
  7 purchase totals = $1,042.00       $1,135.8279   $1,135.82   $1,135.80   $1,135.80