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 $58.35   11.222%   $64.898   $64.90   $64.90   $64.90  
  Purchase #2 $250.70   13.782%   $285.2515   $285.25   $285.25   $285.30  
  Purchase #3 $218.60   13.191%   $247.4355   $247.44   $247.45   $247.40  
  Purchase #4 $57.50   6.270%   $61.1053   $61.11   $61.10   $61.10  
  Purchase #5 $112.77   12.547%   $126.9193   $126.92   $126.90   $126.90  
  Purchase #6 $64.65   8.346%   $70.0457   $70.05   $70.05   $70.00  
  Purchase #7 $195.76   10.589%   $216.489   $216.49   $216.50   $216.50  
  7 purchase totals = $958.33       $1,072.1443   $1,072.16   $1,072.15   $1,072.10