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 $242.71   8.251%   $262.736   $262.74   $262.75   $262.70  
  Purchase #2 $39.60   8.859%   $43.1082   $43.11   $43.10   $43.10  
  Purchase #3 $14.74   3.271%   $15.2221   $15.22   $15.20   $15.20  
  Purchase #4 $205.89   7.380%   $221.0847   $221.08   $221.10   $221.10  
  Purchase #5 $37.44   6.585%   $39.9054   $39.91   $39.90   $39.90  
  Purchase #6 $245.46   9.364%   $268.4449   $268.44   $268.45   $268.40  
  Purchase #7 $161.80   3.325%   $167.1799   $167.18   $167.20   $167.20  
  7 purchase totals = $947.64       $1,017.6812   $1,017.68   $1,017.70   $1,017.60