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 $64.97   6.608%   $69.2632   $69.26   $69.25   $69.30  
  Purchase #2 $23.95   6.384%   $25.479   $25.48   $25.50   $25.50  
  Purchase #3 $180.71   9.282%   $197.4835   $197.48   $197.50   $197.50  
  Purchase #4 $95.56   3.821%   $99.2113   $99.21   $99.20   $99.20  
  Purchase #5 $116.71   11.782%   $130.4608   $130.46   $130.45   $130.50  
  Purchase #6 $238.56   12.394%   $268.1271   $268.13   $268.15   $268.10  
  Purchase #7 $162.72   11.291%   $181.0927   $181.09   $181.10   $181.10  
  7 purchase totals = $883.18       $971.1176   $971.11   $971.15   $971.20