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 $62.44   9.423%   $68.3237   $68.32   $68.30   $68.30  
  Purchase #2 $244.50   6.320%   $259.9524   $259.95   $259.95   $260.00  
  Purchase #3 $112.29   6.760%   $119.8808   $119.88   $119.90   $119.90  
  Purchase #4 $144.37   11.573%   $161.0779   $161.08   $161.10   $161.10  
  Purchase #5 $197.59   7.147%   $211.7118   $211.71   $211.70   $211.70  
  Purchase #6 $187.83   13.107%   $212.4489   $212.45   $212.45   $212.40  
  Purchase #7 $157.36   5.863%   $166.586   $166.59   $166.60   $166.60  
  7 purchase totals = $1,106.38       $1,199.9815   $1,199.98   $1,200.00   $1,200.00