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 $41.54   12.354%   $46.6719   $46.67   $46.65   $46.70  
  Purchase #2 $201.90   4.614%   $211.2157   $211.22   $211.20   $211.20  
  Purchase #3 $128.39   3.734%   $133.1841   $133.18   $133.20   $133.20  
  Purchase #4 $168.84   3.339%   $174.4776   $174.48   $174.50   $174.50  
  Purchase #5 $147.41   8.546%   $160.0077   $160.01   $160.00   $160.00  
  Purchase #6 $46.46   3.322%   $48.0034   $48.00   $48.00   $48.00  
  Purchase #7 $14.72   10.534%   $16.2706   $16.27   $16.25   $16.30  
  7 purchase totals = $749.26       $789.8310   $789.83   $789.80   $789.90