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 $157.26   5.560%   $166.0037   $166.00   $166.00   $166.00  
  Purchase #2 $110.90   8.722%   $120.5727   $120.57   $120.55   $120.60  
  Purchase #3 $128.25   7.109%   $137.3673   $137.37   $137.35   $137.40  
  Purchase #4 $100.50   10.168%   $110.7188   $110.72   $110.70   $110.70  
  Purchase #5 $14.71   10.475%   $16.2509   $16.25   $16.25   $16.30  
  Purchase #6 $22.88   12.812%   $25.8114   $25.81   $25.80   $25.80  
  Purchase #7 $39.34   9.730%   $43.1678   $43.17   $43.15   $43.20  
  7 purchase totals = $573.84       $619.8926   $619.89   $619.80   $620.00