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 $63.50   7.241%   $68.098   $68.10   $68.10   $68.10  
  Purchase #2 $154.27   10.521%   $170.5007   $170.50   $170.50   $170.50  
  Purchase #3 $237.94   3.289%   $245.7658   $245.77   $245.75   $245.80  
  Purchase #4 $130.68   7.836%   $140.9201   $140.92   $140.90   $140.90  
  Purchase #5 $46.66   6.409%   $49.6504   $49.65   $49.65   $49.70  
  Purchase #6 $99.51   10.571%   $110.0292   $110.03   $110.05   $110.00  
  Purchase #7 $216.54   11.452%   $241.3382   $241.34   $241.35   $241.30  
  7 purchase totals = $949.10       $1,026.3024   $1,026.31   $1,026.30   $1,026.30