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 $217.95   11.240%   $242.4476   $242.45   $242.45   $242.40  
  Purchase #2 $138.93   9.778%   $152.5146   $152.51   $152.50   $152.50  
  Purchase #3 $121.88   11.749%   $136.1997   $136.20   $136.20   $136.20  
  Purchase #4 $36.73   6.858%   $39.2489   $39.25   $39.25   $39.20  
  Purchase #5 $82.57   4.168%   $86.0115   $86.01   $86.00   $86.00  
  Purchase #6 $161.36   12.543%   $181.5994   $181.60   $181.60   $181.60  
  Purchase #7 $181.57   3.738%   $188.3571   $188.36   $188.35   $188.40  
  7 purchase totals = $940.99       $1,026.3788   $1,026.38   $1,026.35   $1,026.30