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 $69.77   5.811%   $73.8243   $73.82   $73.80   $73.80  
  Purchase #2 $221.98   4.651%   $232.3043   $232.30   $232.30   $232.30  
  Purchase #3 $218.31   11.789%   $244.0466   $244.05   $244.05   $244.00  
  Purchase #4 $84.35   9.668%   $92.505   $92.51   $92.50   $92.50  
  Purchase #5 $109.41   8.654%   $118.8783   $118.88   $118.90   $118.90  
  Purchase #6 $26.27   12.514%   $29.5574   $29.56   $29.55   $29.60  
  Purchase #7 $183.81   10.709%   $203.4942   $203.49   $203.50   $203.50  
  7 purchase totals = $913.90       $994.6101   $994.61   $994.60   $994.60