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 $244.69   9.801%   $268.6721   $268.67   $268.65   $268.70  
  Purchase #2 $131.98   4.112%   $137.407   $137.41   $137.40   $137.40  
  Purchase #3 $62.83   9.490%   $68.7926   $68.79   $68.80   $68.80  
  Purchase #4 $48.84   7.798%   $52.6485   $52.65   $52.65   $52.60  
  Purchase #5 $193.82   4.161%   $201.8849   $201.88   $201.90   $201.90  
  Purchase #6 $107.50   3.725%   $111.5044   $111.50   $111.50   $111.50  
  Purchase #7 $82.28   4.269%   $85.7925   $85.79   $85.80   $85.80  
  7 purchase totals = $871.94       $926.7020   $926.69   $926.70   $926.70