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 $96.93   5.277%   $102.045   $102.05   $102.05   $102.00  
  Purchase #2 $140.68   12.577%   $158.3733   $158.37   $158.35   $158.40  
  Purchase #3 $34.62   12.755%   $39.0358   $39.04   $39.05   $39.00  
  Purchase #4 $92.33   4.712%   $96.6806   $96.68   $96.70   $96.70  
  Purchase #5 $205.98   10.401%   $227.404   $227.40   $227.40   $227.40  
  Purchase #6 $167.52   6.786%   $178.8879   $178.89   $178.90   $178.90  
  Purchase #7 $235.37   8.870%   $256.2473   $256.25   $256.25   $256.20  
  7 purchase totals = $973.43       $1,058.6739   $1,058.68   $1,058.70   $1,058.60