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 $176.87   6.787%   $188.8742   $188.87   $188.85   $188.90  
  Purchase #2 $80.36   5.470%   $84.7557   $84.76   $84.75   $84.80  
  Purchase #3 $217.27   12.620%   $244.6895   $244.69   $244.70   $244.70  
  Purchase #4 $151.83   8.587%   $164.8676   $164.87   $164.85   $164.90  
  Purchase #5 $132.95   6.155%   $141.1331   $141.13   $141.15   $141.10  
  Purchase #6 $216.52   8.219%   $234.3158   $234.32   $234.30   $234.30  
  Purchase #7 $13.68   8.423%   $14.8323   $14.83   $14.85   $14.80  
  7 purchase totals = $989.48       $1,073.4682   $1,073.47   $1,073.45   $1,073.50