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 $235.58   8.230%   $254.9682   $254.97   $254.95   $255.00  
  Purchase #2 $160.74   8.686%   $174.7019   $174.70   $174.70   $174.70  
  Purchase #3 $176.82   5.410%   $186.386   $186.39   $186.40   $186.40  
  Purchase #4 $91.38   12.415%   $102.7248   $102.72   $102.70   $102.70  
  Purchase #5 $82.90   4.241%   $86.4158   $86.42   $86.40   $86.40  
  Purchase #6 $65.45   11.455%   $72.9473   $72.95   $72.95   $72.90  
  Purchase #7 $230.97   7.740%   $248.8471   $248.85   $248.85   $248.80  
  7 purchase totals = $1,043.84       $1,126.9911   $1,127.00   $1,126.95   $1,126.90