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 $29.76   8.691%   $32.3464   $32.35   $32.35   $32.30  
  Purchase #2 $214.68   10.459%   $237.1334   $237.13   $237.15   $237.10  
  Purchase #3 $205.38   11.431%   $228.857   $228.86   $228.85   $228.90  
  Purchase #4 $226.43   9.770%   $248.5522   $248.55   $248.55   $248.60  
  Purchase #5 $92.89   9.526%   $101.7387   $101.74   $101.75   $101.70  
  Purchase #6 $162.73   9.760%   $178.6124   $178.61   $178.60   $178.60  
  Purchase #7 $128.42   7.620%   $138.2056   $138.21   $138.20   $138.20  
  7 purchase totals = $1,060.29       $1,165.4457   $1,165.45   $1,165.45   $1,165.40