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 $202.29   13.295%   $229.1845   $229.18   $229.20   $229.20  
  Purchase #2 $94.91   4.104%   $98.8051   $98.81   $98.80   $98.80  
  Purchase #3 $72.63   11.676%   $81.1103   $81.11   $81.10   $81.10  
  Purchase #4 $109.34   12.474%   $122.9791   $122.98   $123.00   $123.00  
  Purchase #5 $180.96   8.867%   $197.0057   $197.01   $197.00   $197.00  
  Purchase #6 $157.28   11.760%   $175.7761   $175.78   $175.80   $175.80  
  Purchase #7 $77.79   5.407%   $81.9961   $82.00   $82.00   $82.00  
  7 purchase totals = $895.20       $986.8569   $986.87   $986.90   $986.90