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 $186.43   5.622%   $196.9111   $196.91   $196.90   $196.90  
  Purchase #2 $182.49   12.166%   $204.6917   $204.69   $204.70   $204.70  
  Purchase #3 $126.83   7.787%   $136.7063   $136.71   $136.70   $136.70  
  Purchase #4 $178.62   12.665%   $201.2422   $201.24   $201.25   $201.20  
  Purchase #5 $102.35   8.362%   $110.9085   $110.91   $110.90   $110.90  
  Purchase #6 $202.62   4.252%   $211.2354   $211.24   $211.25   $211.20  
  Purchase #7 $18.60   11.184%   $20.6802   $20.68   $20.70   $20.70  
  7 purchase totals = $997.94       $1,082.3754   $1,082.38   $1,082.40   $1,082.30