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 $212.36   6.461%   $226.0806   $226.08   $226.10   $226.10  
  Purchase #2 $172.61   9.370%   $188.7836   $188.78   $188.80   $188.80  
  Purchase #3 $95.95   9.532%   $105.096   $105.10   $105.10   $105.10  
  Purchase #4 $247.61   6.823%   $264.5044   $264.50   $264.50   $264.50  
  Purchase #5 $172.41   11.438%   $192.1303   $192.13   $192.15   $192.10  
  Purchase #6 $49.66   9.841%   $54.547   $54.55   $54.55   $54.50  
  Purchase #7 $35.53   7.545%   $38.2107   $38.21   $38.20   $38.20  
  7 purchase totals = $986.13       $1,069.3526   $1,069.35   $1,069.40   $1,069.30