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 $58.64   3.391%   $60.6285   $60.63   $60.65   $60.60  
  Purchase #2 $88.85   7.113%   $95.1699   $95.17   $95.15   $95.20  
  Purchase #3 $145.69   13.121%   $164.806   $164.81   $164.80   $164.80  
  Purchase #4 $94.46   3.669%   $97.9257   $97.93   $97.95   $97.90  
  Purchase #5 $92.72   10.317%   $102.2859   $102.29   $102.30   $102.30  
  Purchase #6 $202.89   6.564%   $216.2077   $216.21   $216.20   $216.20  
  Purchase #7 $154.32   8.302%   $167.1316   $167.13   $167.15   $167.10  
  7 purchase totals = $837.57       $904.1553   $904.17   $904.20   $904.10