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 $54.64   11.525%   $60.9373   $60.94   $60.95   $60.90  
  Purchase #2 $202.62   6.850%   $216.4995   $216.50   $216.50   $216.50  
  Purchase #3 $230.53   10.510%   $254.7587   $254.76   $254.75   $254.80  
  Purchase #4 $77.74   11.501%   $86.6809   $86.68   $86.70   $86.70  
  Purchase #5 $123.28   3.418%   $127.4937   $127.49   $127.50   $127.50  
  Purchase #6 $249.97   13.364%   $283.376   $283.38   $283.40   $283.40  
  Purchase #7 $223.76   6.320%   $237.9016   $237.90   $237.90   $237.90  
  7 purchase totals = $1,162.54       $1,267.6477   $1,267.65   $1,267.70   $1,267.70