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 $68.72   11.717%   $76.7719   $76.77   $76.75   $76.80  
  Purchase #2 $144.94   6.781%   $154.7684   $154.77   $154.75   $154.80  
  Purchase #3 $200.34   11.308%   $222.9944   $222.99   $223.00   $223.00  
  Purchase #4 $165.75   4.831%   $173.7574   $173.76   $173.75   $173.80  
  Purchase #5 $213.58   8.755%   $232.2789   $232.28   $232.30   $232.30  
  Purchase #6 $62.43   10.153%   $68.7685   $68.77   $68.75   $68.80  
  Purchase #7 $84.53   5.725%   $89.3693   $89.37   $89.35   $89.40  
  7 purchase totals = $940.29       $1,018.7088   $1,018.71   $1,018.65   $1,018.90