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 $61.39   5.871%   $64.9942   $64.99   $65.00   $65.00  
  Purchase #2 $236.67   9.588%   $259.3619   $259.36   $259.35   $259.40  
  Purchase #3 $43.40   11.319%   $48.3124   $48.31   $48.30   $48.30  
  Purchase #4 $71.56   5.586%   $75.5573   $75.56   $75.55   $75.60  
  Purchase #5 $27.93   4.460%   $29.1757   $29.18   $29.20   $29.20  
  Purchase #6 $136.74   9.248%   $149.3857   $149.39   $149.40   $149.40  
  Purchase #7 $235.25   7.264%   $252.3386   $252.34   $252.35   $252.30  
  7 purchase totals = $812.94       $879.1258   $879.13   $879.15   $879.20