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 $214.32   8.595%   $232.7408   $232.74   $232.75   $232.70  
  Purchase #2 $210.35   10.693%   $232.8427   $232.84   $232.85   $232.80  
  Purchase #3 $33.85   5.642%   $35.7598   $35.76   $35.75   $35.80  
  Purchase #4 $228.91   7.346%   $245.7257   $245.73   $245.75   $245.70  
  Purchase #5 $216.53   12.659%   $243.9405   $243.94   $243.95   $243.90  
  Purchase #6 $152.29   4.541%   $159.2055   $159.21   $159.20   $159.20  
  Purchase #7 $158.61   5.512%   $167.3526   $167.35   $167.35   $167.40  
  7 purchase totals = $1,214.86       $1,317.5676   $1,317.57   $1,317.60   $1,317.50