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 $90.93   5.374%   $95.8166   $95.82   $95.80   $95.80  
  Purchase #2 $44.46   4.225%   $46.3384   $46.34   $46.35   $46.30  
  Purchase #3 $118.47   7.544%   $127.4074   $127.41   $127.40   $127.40  
  Purchase #4 $192.54   13.227%   $218.0073   $218.01   $218.00   $218.00  
  Purchase #5 $34.56   13.855%   $39.3483   $39.35   $39.35   $39.30  
  Purchase #6 $209.40   12.461%   $235.4933   $235.49   $235.50   $235.50  
  Purchase #7 $199.37   12.527%   $224.3451   $224.35   $224.35   $224.30  
  7 purchase totals = $889.73       $986.7564   $986.77   $986.75   $986.60