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 $174.97   13.532%   $198.6469   $198.65   $198.65   $198.60  
  Purchase #2 $105.55   11.511%   $117.6999   $117.70   $117.70   $117.70  
  Purchase #3 $191.76   11.217%   $213.2697   $213.27   $213.25   $213.30  
  Purchase #4 $218.98   12.448%   $246.2386   $246.24   $246.25   $246.20  
  Purchase #5 $14.31   13.650%   $16.2633   $16.26   $16.25   $16.30  
  Purchase #6 $33.79   3.502%   $34.9733   $34.97   $34.95   $35.00  
  Purchase #7 $179.78   12.379%   $202.035   $202.04   $202.05   $202.00  
  7 purchase totals = $919.14       $1,029.1267   $1,029.13   $1,029.10   $1,029.10