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 $56.42   4.463%   $58.938   $58.94   $58.95   $58.90  
  Purchase #2 $190.51   5.595%   $201.169   $201.17   $201.15   $201.20  
  Purchase #3 $156.73   8.868%   $170.6288   $170.63   $170.65   $170.60  
  Purchase #4 $184.71   12.368%   $207.5549   $207.55   $207.55   $207.60  
  Purchase #5 $43.75   3.117%   $45.1137   $45.11   $45.10   $45.10  
  Purchase #6 $171.48   12.806%   $193.4397   $193.44   $193.45   $193.40  
  Purchase #7 $82.84   8.689%   $90.038   $90.04   $90.05   $90.00  
  7 purchase totals = $886.44       $966.8821   $966.88   $966.90   $966.80