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 $149.50   10.187%   $164.7296   $164.73   $164.75   $164.70  
  Purchase #2 $243.46   5.696%   $257.3275   $257.33   $257.35   $257.30  
  Purchase #3 $170.33   3.561%   $176.3955   $176.40   $176.40   $176.40  
  Purchase #4 $247.35   8.762%   $269.0228   $269.02   $269.00   $269.00  
  Purchase #5 $27.49   7.359%   $29.513   $29.51   $29.50   $29.50  
  Purchase #6 $17.86   12.298%   $20.0564   $20.06   $20.05   $20.10  
  Purchase #7 $107.52   3.644%   $111.438   $111.44   $111.45   $111.40  
  7 purchase totals = $963.51       $1,028.4828   $1,028.49   $1,028.50   $1,028.40