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 $206.87   9.713%   $226.9633   $226.96   $226.95   $227.00  
  Purchase #2 $61.69   7.663%   $66.4173   $66.42   $66.40   $66.40  
  Purchase #3 $211.60   7.440%   $227.343   $227.34   $227.35   $227.30  
  Purchase #4 $56.82   11.651%   $63.4401   $63.44   $63.45   $63.40  
  Purchase #5 $159.85   4.162%   $166.503   $166.50   $166.50   $166.50  
  Purchase #6 $110.26   9.362%   $120.5825   $120.58   $120.60   $120.60  
  Purchase #7 $215.92   7.615%   $232.3623   $232.36   $232.35   $232.40  
  7 purchase totals = $1,023.01       $1,103.6115   $1,103.60   $1,103.60   $1,103.60