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 $155.28   11.561%   $173.2319   $173.23   $173.25   $173.20  
  Purchase #2 $97.55   4.197%   $101.6442   $101.64   $101.65   $101.60  
  Purchase #3 $90.95   6.550%   $96.9072   $96.91   $96.90   $96.90  
  Purchase #4 $231.26   3.750%   $239.9323   $239.93   $239.95   $239.90  
  Purchase #5 $117.45   4.235%   $122.424   $122.42   $122.40   $122.40  
  Purchase #6 $148.59   13.762%   $169.039   $169.04   $169.05   $169.00  
  Purchase #7 $177.83   7.663%   $191.4571   $191.46   $191.45   $191.50  
  7 purchase totals = $1,018.91       $1,094.6357   $1,094.63   $1,094.65   $1,094.50