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 $63.95   13.540%   $72.6088   $72.61   $72.60   $72.60  
  Purchase #2 $77.84   8.155%   $84.1879   $84.19   $84.20   $84.20  
  Purchase #3 $84.33   13.559%   $95.7643   $95.76   $95.75   $95.80  
  Purchase #4 $178.36   5.351%   $187.904   $187.90   $187.90   $187.90  
  Purchase #5 $6.97   8.773%   $7.5815   $7.58   $7.60   $7.60  
  Purchase #6 $243.25   5.283%   $256.1009   $256.10   $256.10   $256.10  
  Purchase #7 $209.92   6.235%   $223.0085   $223.01   $223.00   $223.00  
  7 purchase totals = $864.62       $927.1559   $927.15   $927.15   $927.20