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 $31.61   13.867%   $35.9934   $35.99   $36.00   $36.00  
  Purchase #2 $191.43   13.116%   $216.538   $216.54   $216.55   $216.50  
  Purchase #3 $50.46   4.171%   $52.5647   $52.56   $52.55   $52.60  
  Purchase #4 $146.52   12.783%   $165.2497   $165.25   $165.25   $165.20  
  Purchase #5 $184.32   11.163%   $204.8956   $204.90   $204.90   $204.90  
  Purchase #6 $20.84   12.596%   $23.465   $23.47   $23.45   $23.50  
  Purchase #7 $205.44   4.754%   $215.2066   $215.21   $215.20   $215.20  
  7 purchase totals = $830.62       $913.9130   $913.92   $913.90   $913.90