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 $181.49   8.257%   $196.4756   $196.48   $196.50   $196.50  
  Purchase #2 $60.64   11.535%   $67.6348   $67.63   $67.65   $67.60  
  Purchase #3 $84.72   10.432%   $93.558   $93.56   $93.55   $93.60  
  Purchase #4 $193.34   9.256%   $211.2356   $211.24   $211.25   $211.20  
  Purchase #5 $130.54   11.385%   $145.402   $145.40   $145.40   $145.40  
  Purchase #6 $84.44   4.216%   $88   $88.00   $88.00   $88.00  
  Purchase #7 $57.66   12.760%   $65.0174   $65.02   $65.00   $65.00  
  7 purchase totals = $792.83       $867.3234   $867.33   $867.35   $867.30