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 $153.74   8.723%   $167.1507   $167.15   $167.15   $167.20  
  Purchase #2 $98.67   13.297%   $111.7901   $111.79   $111.80   $111.80  
  Purchase #3 $183.82   7.613%   $197.8142   $197.81   $197.80   $197.80  
  Purchase #4 $182.77   11.480%   $203.752   $203.75   $203.75   $203.80  
  Purchase #5 $235.61   13.354%   $267.0734   $267.07   $267.05   $267.10  
  Purchase #6 $87.74   3.298%   $90.6337   $90.63   $90.65   $90.60  
  Purchase #7 $219.80   3.228%   $226.8951   $226.90   $226.90   $226.90  
  7 purchase totals = $1,162.15       $1,265.1092   $1,265.10   $1,265.10   $1,265.20