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 $185.36   6.571%   $197.54   $197.54   $197.55   $197.50  
  Purchase #2 $62.71   5.318%   $66.0449   $66.04   $66.05   $66.00  
  Purchase #3 $19.59   5.787%   $20.7237   $20.72   $20.70   $20.70  
  Purchase #4 $236.67   13.740%   $269.1885   $269.19   $269.20   $269.20  
  Purchase #5 $215.89   8.643%   $234.5494   $234.55   $234.55   $234.50  
  Purchase #6 $11.56   5.664%   $12.2148   $12.21   $12.20   $12.20  
  Purchase #7 $204.92   7.769%   $220.8402   $220.84   $220.85   $220.80  
  7 purchase totals = $936.70       $1,021.1015   $1,021.09   $1,021.10   $1,020.90