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 $125.77   6.596%   $134.0658   $134.07   $134.05   $134.10  
  Purchase #2 $45.64   6.384%   $48.5537   $48.55   $48.55   $48.60  
  Purchase #3 $121.35   3.571%   $125.6834   $125.68   $125.70   $125.70  
  Purchase #4 $201.27   7.762%   $216.8926   $216.89   $216.90   $216.90  
  Purchase #5 $81.91   4.655%   $85.7229   $85.72   $85.70   $85.70  
  Purchase #6 $169.41   8.629%   $184.0284   $184.03   $184.05   $184.00  
  Purchase #7 $128.70   4.633%   $134.6627   $134.66   $134.65   $134.70  
  7 purchase totals = $874.05       $929.6095   $929.60   $929.60   $929.70