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 $181.88   5.298%   $191.516   $191.52   $191.50   $191.50  
  Purchase #2 $171.42   10.444%   $189.3231   $189.32   $189.30   $189.30  
  Purchase #3 $244.53   7.213%   $262.1679   $262.17   $262.15   $262.20  
  Purchase #4 $124.95   6.429%   $132.983   $132.98   $133.00   $133.00  
  Purchase #5 $201.92   6.478%   $215.0004   $215.00   $215.00   $215.00  
  Purchase #6 $165.37   8.351%   $179.18   $179.18   $179.20   $179.20  
  Purchase #7 $47.30   4.664%   $49.5061   $49.51   $49.50   $49.50  
  7 purchase totals = $1,137.37       $1,219.6765   $1,219.68   $1,219.65   $1,219.70