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 $59.65   11.364%   $66.4286   $66.43   $66.45   $66.40  
  Purchase #2 $174.73   7.449%   $187.7456   $187.75   $187.75   $187.70  
  Purchase #3 $218.71   6.528%   $232.9874   $232.99   $233.00   $233.00  
  Purchase #4 $80.80   7.848%   $87.1412   $87.14   $87.15   $87.10  
  Purchase #5 $118.67   11.586%   $132.4191   $132.42   $132.40   $132.40  
  Purchase #6 $117.71   3.635%   $121.9888   $121.99   $122.00   $122.00  
  Purchase #7 $33.38   7.146%   $35.7653   $35.77   $35.75   $35.80  
  7 purchase totals = $803.65       $864.4760   $864.49   $864.50   $864.40