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 $68.37   9.676%   $74.9855   $74.99   $75.00   $75.00  
  Purchase #2 $115.65   13.720%   $131.5172   $131.52   $131.50   $131.50  
  Purchase #3 $76.41   13.829%   $86.9767   $86.98   $87.00   $87.00  
  Purchase #4 $80.65   10.418%   $89.0521   $89.05   $89.05   $89.10  
  Purchase #5 $198.25   5.806%   $209.7604   $209.76   $209.75   $209.80  
  Purchase #6 $168.59   11.482%   $187.9475   $187.95   $187.95   $187.90  
  Purchase #7 $175.69   10.805%   $194.6733   $194.67   $194.65   $194.70  
  7 purchase totals = $883.61       $974.9127   $974.92   $974.90   $975.00