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 $53.89   5.366%   $56.7817   $56.78   $56.80   $56.80  
  Purchase #2 $189.66   12.655%   $213.6615   $213.66   $213.65   $213.70  
  Purchase #3 $104.44   4.163%   $108.7878   $108.79   $108.80   $108.80  
  Purchase #4 $119.63   9.105%   $130.5223   $130.52   $130.50   $130.50  
  Purchase #5 $141.99   6.343%   $150.9964   $151.00   $151.00   $151.00  
  Purchase #6 $146.64   13.606%   $166.5918   $166.59   $166.60   $166.60  
  Purchase #7 $211.64   6.725%   $225.8728   $225.87   $225.85   $225.90  
  7 purchase totals = $967.89       $1,053.2143   $1,053.21   $1,053.20   $1,053.30