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 $228.93   8.416%   $248.1967   $248.20   $248.20   $248.20  
  Purchase #2 $174.78   9.136%   $190.7479   $190.75   $190.75   $190.70  
  Purchase #3 $144.50   7.395%   $155.1858   $155.19   $155.20   $155.20  
  Purchase #4 $77.25   9.819%   $84.8352   $84.84   $84.85   $84.80  
  Purchase #5 $30.97   7.691%   $33.3519   $33.35   $33.35   $33.40  
  Purchase #6 $148.37   8.104%   $160.3939   $160.39   $160.40   $160.40  
  Purchase #7 $211.27   12.214%   $237.0745   $237.07   $237.05   $237.10  
  7 purchase totals = $1,016.07       $1,109.7859   $1,109.79   $1,109.80   $1,109.80