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 $57.28   6.824%   $61.1888   $61.19   $61.20   $61.20  
  Purchase #2 $187.31   5.766%   $198.1103   $198.11   $198.10   $198.10  
  Purchase #3 $32.48   13.561%   $36.8846   $36.88   $36.90   $36.90  
  Purchase #4 $29.31   5.726%   $30.9883   $30.99   $31.00   $31.00  
  Purchase #5 $182.78   12.440%   $205.5178   $205.52   $205.50   $205.50  
  Purchase #6 $86.90   13.383%   $98.5298   $98.53   $98.55   $98.50  
  Purchase #7 $219.58   11.349%   $244.5001   $244.50   $244.50   $244.50  
  7 purchase totals = $795.64       $875.7197   $875.72   $875.75   $875.70