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 $46.82   11.139%   $52.0353   $52.04   $52.05   $52.00  
  Purchase #2 $162.33   3.814%   $168.5213   $168.52   $168.50   $168.50  
  Purchase #3 $239.57   11.807%   $267.856   $267.86   $267.85   $267.90  
  Purchase #4 $67.30   3.717%   $69.8015   $69.80   $69.80   $69.80  
  Purchase #5 $41.62   12.698%   $46.9049   $46.90   $46.90   $46.90  
  Purchase #6 $138.57   9.255%   $151.3947   $151.39   $151.40   $151.40  
  Purchase #7 $193.72   8.490%   $210.1668   $210.17   $210.15   $210.20  
  7 purchase totals = $889.93       $966.6805   $966.68   $966.65   $966.70