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 $85.61   10.123%   $94.2763   $94.28   $94.30   $94.30  
  Purchase #2 $161.36   6.270%   $171.4773   $171.48   $171.50   $171.50  
  Purchase #3 $48.62   3.531%   $50.3368   $50.34   $50.35   $50.30  
  Purchase #4 $148.49   11.118%   $164.9991   $165.00   $165.00   $165.00  
  Purchase #5 $241.94   9.503%   $264.9316   $264.93   $264.95   $264.90  
  Purchase #6 $224.77   8.867%   $244.7004   $244.70   $244.70   $244.70  
  Purchase #7 $68.28   9.767%   $74.9489   $74.95   $74.95   $74.90  
  7 purchase totals = $979.07       $1,065.6704   $1,065.68   $1,065.75   $1,065.60