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 $175.87   10.698%   $194.6846   $194.68   $194.70   $194.70  
  Purchase #2 $20.45   11.161%   $22.7324   $22.73   $22.75   $22.70  
  Purchase #3 $66.36   6.103%   $70.41   $70.41   $70.40   $70.40  
  Purchase #4 $34.69   12.625%   $39.0696   $39.07   $39.05   $39.10  
  Purchase #5 $215.65   5.682%   $227.9032   $227.90   $227.90   $227.90  
  Purchase #6 $106.86   12.212%   $119.9097   $119.91   $119.90   $119.90  
  Purchase #7 $228.88   9.764%   $251.2278   $251.23   $251.25   $251.20  
  7 purchase totals = $848.76       $925.9373   $925.93   $925.95   $925.90