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 $150.54   11.751%   $168.23   $168.23   $168.25   $168.20  
  Purchase #2 $194.58   5.846%   $205.9551   $205.96   $205.95   $206.00  
  Purchase #3 $92.79   10.164%   $102.2212   $102.22   $102.20   $102.20  
  Purchase #4 $242.77   10.776%   $268.9309   $268.93   $268.95   $268.90  
  Purchase #5 $50.33   5.331%   $53.0131   $53.01   $53.00   $53.00  
  Purchase #6 $195.78   8.685%   $212.7835   $212.78   $212.80   $212.80  
  Purchase #7 $9.62   6.448%   $10.2403   $10.24   $10.25   $10.20  
  7 purchase totals = $936.41       $1,021.3741   $1,021.37   $1,021.40   $1,021.30