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 $42.57   11.864%   $47.6205   $47.62   $47.60   $47.60  
  Purchase #2 $152.69   8.642%   $165.8855   $165.89   $165.90   $165.90  
  Purchase #3 $32.95   6.287%   $35.0216   $35.02   $35.00   $35.00  
  Purchase #4 $40.28   11.668%   $44.9799   $44.98   $45.00   $45.00  
  Purchase #5 $114.50   5.604%   $120.9166   $120.92   $120.90   $120.90  
  Purchase #6 $163.75   12.794%   $184.7002   $184.70   $184.70   $184.70  
  Purchase #7 $147.32   7.251%   $158.0022   $158.00   $158.00   $158.00  
  7 purchase totals = $694.06       $757.1265   $757.13   $757.10   $757.10