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 $56.77   9.176%   $61.9792   $61.98   $62.00   $62.00  
  Purchase #2 $15.67   10.236%   $17.274   $17.27   $17.25   $17.30  
  Purchase #3 $160.40   8.683%   $174.3275   $174.33   $174.35   $174.30  
  Purchase #4 $25.40   11.254%   $28.2585   $28.26   $28.25   $28.30  
  Purchase #5 $191.66   10.287%   $211.3761   $211.38   $211.40   $211.40  
  Purchase #6 $23.99   5.344%   $25.272   $25.27   $25.25   $25.30  
  Purchase #7 $235.70   8.407%   $255.5153   $255.52   $255.50   $255.50  
  7 purchase totals = $709.59       $774.0026   $774.01   $774.00   $774.10