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 $42.53   4.856%   $44.5953   $44.60   $44.60   $44.60  
  Purchase #2 $70.37   10.610%   $77.8363   $77.84   $77.85   $77.80  
  Purchase #3 $93.34   13.802%   $106.2228   $106.22   $106.20   $106.20  
  Purchase #4 $227.94   9.560%   $249.7311   $249.73   $249.75   $249.70  
  Purchase #5 $191.90   5.174%   $201.8289   $201.83   $201.85   $201.80  
  Purchase #6 $64.87   10.862%   $71.9162   $71.92   $71.90   $71.90  
  Purchase #7 $136.65   10.190%   $150.5746   $150.57   $150.55   $150.60  
  7 purchase totals = $827.60       $902.7052   $902.71   $902.70   $902.60