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 $85.91   12.450%   $96.6058   $96.61   $96.60   $96.60  
  Purchase #2 $170.45   4.812%   $178.6521   $178.65   $178.65   $178.70  
  Purchase #3 $225.77   3.713%   $234.1528   $234.15   $234.15   $234.20  
  Purchase #4 $66.61   4.818%   $69.8193   $69.82   $69.80   $69.80  
  Purchase #5 $5.75   3.463%   $5.9491   $5.95   $5.95   $5.90  
  Purchase #6 $203.42   3.684%   $210.914   $210.91   $210.90   $210.90  
  Purchase #7 $171.28   6.741%   $182.826   $182.83   $182.85   $182.80  
  7 purchase totals = $929.19       $978.9191   $978.92   $978.90   $978.90