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 $61.84   9.343%   $67.6177   $67.62   $67.60   $67.60  
  Purchase #2 $186.38   10.132%   $205.264   $205.26   $205.25   $205.30  
  Purchase #3 $243.65   10.740%   $269.818   $269.82   $269.80   $269.80  
  Purchase #4 $27.63   3.429%   $28.5774   $28.58   $28.60   $28.60  
  Purchase #5 $208.33   5.421%   $219.6236   $219.62   $219.60   $219.60  
  Purchase #6 $25.40   10.509%   $28.0693   $28.07   $28.05   $28.10  
  Purchase #7 $112.41   10.331%   $124.0231   $124.02   $124.00   $124.00  
  7 purchase totals = $865.64       $942.9931   $942.99   $942.90   $943.00