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 $224.38   10.471%   $247.8748   $247.87   $247.85   $247.90  
  Purchase #2 $67.33   12.803%   $75.9503   $75.95   $75.95   $76.00  
  Purchase #3 $11.52   5.683%   $12.1747   $12.17   $12.15   $12.20  
  Purchase #4 $95.65   10.171%   $105.3786   $105.38   $105.40   $105.40  
  Purchase #5 $67.55   13.620%   $76.7503   $76.75   $76.75   $76.80  
  Purchase #6 $200.74   9.460%   $219.73   $219.73   $219.75   $219.70  
  Purchase #7 $24.59   6.569%   $26.2053   $26.21   $26.20   $26.20  
  7 purchase totals = $691.76       $764.0640   $764.06   $764.05   $764.20