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 $70.84   5.634%   $74.8311   $74.83   $74.85   $74.80  
  Purchase #2 $6.36   7.797%   $6.8559   $6.86   $6.85   $6.90  
  Purchase #3 $92.56   8.704%   $100.6164   $100.62   $100.60   $100.60  
  Purchase #4 $189.58   9.620%   $207.8176   $207.82   $207.80   $207.80  
  Purchase #5 $147.69   3.513%   $152.8783   $152.88   $152.90   $152.90  
  Purchase #6 $133.62   9.676%   $146.5491   $146.55   $146.55   $146.50  
  Purchase #7 $106.81   5.159%   $112.3203   $112.32   $112.30   $112.30  
  7 purchase totals = $747.46       $801.8687   $801.88   $801.85   $801.80