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 $167.39   10.475%   $184.9241   $184.92   $184.90   $184.90  
  Purchase #2 $250.38   7.381%   $268.8605   $268.86   $268.85   $268.90  
  Purchase #3 $14.31   7.481%   $15.3805   $15.38   $15.40   $15.40  
  Purchase #4 $45.62   6.301%   $48.4945   $48.49   $48.50   $48.50  
  Purchase #5 $162.48   10.288%   $179.1959   $179.20   $179.20   $179.20  
  Purchase #6 $28.63   10.348%   $31.5926   $31.59   $31.60   $31.60  
  Purchase #7 $137.71   5.869%   $145.7922   $145.79   $145.80   $145.80  
  7 purchase totals = $806.52       $874.2403   $874.23   $874.25   $874.30