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 $32.89   4.124%   $34.2464   $34.25   $34.25   $34.20  
  Purchase #2 $190.38   12.751%   $214.6554   $214.66   $214.65   $214.70  
  Purchase #3 $220.30   7.703%   $237.2697   $237.27   $237.25   $237.30  
  Purchase #4 $241.92   9.414%   $264.6943   $264.69   $264.70   $264.70  
  Purchase #5 $43.42   8.187%   $46.9748   $46.97   $46.95   $47.00  
  Purchase #6 $197.74   13.135%   $223.7131   $223.71   $223.70   $223.70  
  Purchase #7 $27.83   12.728%   $31.3722   $31.37   $31.35   $31.40  
  7 purchase totals = $954.48       $1,052.9259   $1,052.92   $1,052.85   $1,053.00