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 $110.44   4.735%   $115.6693   $115.67   $115.65   $115.70  
  Purchase #2 $140.33   5.371%   $147.8671   $147.87   $147.85   $147.90  
  Purchase #3 $20.26   8.764%   $22.0356   $22.04   $22.05   $22.00  
  Purchase #4 $118.48   8.839%   $128.9524   $128.95   $128.95   $129.00  
  Purchase #5 $36.26   10.142%   $39.9375   $39.94   $39.95   $39.90  
  Purchase #6 $98.48   12.371%   $110.663   $110.66   $110.65   $110.70  
  Purchase #7 $20.25   7.118%   $21.6914   $21.69   $21.70   $21.70  
  7 purchase totals = $544.50       $586.8163   $586.82   $586.80   $586.90