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 $124.51   13.259%   $141.0188   $141.02   $141.00   $141.00  
  Purchase #2 $14.57   10.695%   $16.1283   $16.13   $16.15   $16.10  
  Purchase #3 $70.47   7.602%   $75.8271   $75.83   $75.85   $75.80  
  Purchase #4 $191.68   8.826%   $208.5977   $208.60   $208.60   $208.60  
  Purchase #5 $31.78   13.207%   $35.9772   $35.98   $36.00   $36.00  
  Purchase #6 $133.42   9.173%   $145.6586   $145.66   $145.65   $145.70  
  Purchase #7 $150.66   12.180%   $169.0104   $169.01   $169.00   $169.00  
  7 purchase totals = $717.09       $792.2181   $792.23   $792.25   $792.20