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 $67.86   12.766%   $76.523   $76.52   $76.50   $76.50  
  Purchase #2 $242.59   11.163%   $269.6703   $269.67   $269.65   $269.70  
  Purchase #3 $40.88   8.478%   $44.3458   $44.35   $44.35   $44.30  
  Purchase #4 $232.43   10.630%   $257.1373   $257.14   $257.15   $257.10  
  Purchase #5 $194.36   3.462%   $201.0887   $201.09   $201.10   $201.10  
  Purchase #6 $153.72   5.826%   $162.6757   $162.68   $162.70   $162.70  
  Purchase #7 $60.66   12.848%   $68.4536   $68.45   $68.45   $68.50  
  7 purchase totals = $992.50       $1,079.8944   $1,079.90   $1,079.90   $1,079.90