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 $207.79   12.374%   $233.5019   $233.50   $233.50   $233.50  
  Purchase #2 $113.48   7.845%   $122.3825   $122.38   $122.40   $122.40  
  Purchase #3 $131.99   9.807%   $144.9343   $144.93   $144.95   $144.90  
  Purchase #4 $145.59   13.106%   $164.671   $164.67   $164.65   $164.70  
  Purchase #5 $57.94   13.427%   $65.7196   $65.72   $65.70   $65.70  
  Purchase #6 $175.61   3.655%   $182.0285   $182.03   $182.05   $182.00  
  Purchase #7 $181.31   11.288%   $201.7763   $201.78   $201.80   $201.80  
  7 purchase totals = $1,013.71       $1,115.0141   $1,115.01   $1,115.05   $1,115.00