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 $174.99   7.649%   $188.375   $188.38   $188.40   $188.40  
  Purchase #2 $207.48   13.292%   $235.0582   $235.06   $235.05   $235.10  
  Purchase #3 $29.82   5.543%   $31.4729   $31.47   $31.45   $31.50  
  Purchase #4 $109.79   11.243%   $122.1337   $122.13   $122.15   $122.10  
  Purchase #5 $210.56   7.593%   $226.5478   $226.55   $226.55   $226.50  
  Purchase #6 $137.31   7.140%   $147.1139   $147.11   $147.10   $147.10  
  Purchase #7 $201.85   8.610%   $219.2293   $219.23   $219.25   $219.20  
  7 purchase totals = $1,071.80       $1,169.9308   $1,169.93   $1,169.95   $1,169.90