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 $41.27   7.188%   $44.2365   $44.24   $44.25   $44.20  
  Purchase #2 $147.59   4.420%   $154.1135   $154.11   $154.10   $154.10  
  Purchase #3 $18.46   5.518%   $19.4786   $19.48   $19.50   $19.50  
  Purchase #4 $181.47   11.843%   $202.9615   $202.96   $202.95   $203.00  
  Purchase #5 $85.39   11.794%   $95.4609   $95.46   $95.45   $95.50  
  Purchase #6 $154.27   4.518%   $161.2399   $161.24   $161.25   $161.20  
  Purchase #7 $128.49   13.248%   $145.5124   $145.51   $145.50   $145.50  
  7 purchase totals = $756.94       $823.0033   $823.00   $823.00   $823.00