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 $205.67   9.527%   $225.2642   $225.26   $225.25   $225.30  
  Purchase #2 $61.79   5.733%   $65.3324   $65.33   $65.35   $65.30  
  Purchase #3 $165.45   12.190%   $185.6184   $185.62   $185.60   $185.60  
  Purchase #4 $135.91   8.418%   $147.3509   $147.35   $147.35   $147.40  
  Purchase #5 $218.84   3.740%   $227.0246   $227.02   $227.00   $227.00  
  Purchase #6 $40.95   12.487%   $46.0634   $46.06   $46.05   $46.10  
  Purchase #7 $126.45   5.780%   $133.7588   $133.76   $133.75   $133.80  
  7 purchase totals = $955.06       $1,030.4127   $1,030.40   $1,030.35   $1,030.50