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 $65.98   11.852%   $73.7999   $73.80   $73.80   $73.80  
  Purchase #2 $102.32   6.295%   $108.761   $108.76   $108.75   $108.80  
  Purchase #3 $66.35   4.318%   $69.215   $69.22   $69.20   $69.20  
  Purchase #4 $47.86   11.797%   $53.506   $53.51   $53.50   $53.50  
  Purchase #5 $105.56   5.299%   $111.1536   $111.15   $111.15   $111.20  
  Purchase #6 $126.33   11.362%   $140.6836   $140.68   $140.70   $140.70  
  Purchase #7 $202.96   8.276%   $219.757   $219.76   $219.75   $219.80  
  7 purchase totals = $717.36       $776.8761   $776.88   $776.85   $777.00