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 $246.38   8.717%   $267.8569   $267.86   $267.85   $267.90  
  Purchase #2 $6.69   7.394%   $7.1847   $7.18   $7.20   $7.20  
  Purchase #3 $176.48   6.324%   $187.6406   $187.64   $187.65   $187.60  
  Purchase #4 $203.65   12.126%   $228.3446   $228.34   $228.35   $228.30  
  Purchase #5 $180.94   11.163%   $201.1383   $201.14   $201.15   $201.10  
  Purchase #6 $83.61   5.835%   $88.4886   $88.49   $88.50   $88.50  
  Purchase #7 $76.52   6.293%   $81.3354   $81.34   $81.35   $81.30  
  7 purchase totals = $974.27       $1,061.9891   $1,061.99   $1,062.05   $1,061.90