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 $249.93   7.675%   $269.1121   $269.11   $269.10   $269.10  
  Purchase #2 $182.47   10.144%   $200.9798   $200.98   $201.00   $201.00  
  Purchase #3 $24.27   9.727%   $26.6307   $26.63   $26.65   $26.60  
  Purchase #4 $195.70   9.266%   $213.8336   $213.83   $213.85   $213.80  
  Purchase #5 $48.52   12.243%   $54.4603   $54.46   $54.45   $54.50  
  Purchase #6 $31.40   10.399%   $34.6653   $34.67   $34.65   $34.70  
  Purchase #7 $165.72   10.821%   $183.6526   $183.65   $183.65   $183.70  
  7 purchase totals = $898.01       $983.3344   $983.33   $983.35   $983.40