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 $190.66   4.661%   $199.5467   $199.55   $199.55   $199.50  
  Purchase #2 $229.35   9.195%   $250.4387   $250.44   $250.45   $250.40  
  Purchase #3 $248.34   8.154%   $268.5896   $268.59   $268.60   $268.60  
  Purchase #4 $225.57   10.424%   $249.0834   $249.08   $249.10   $249.10  
  Purchase #5 $249.75   5.473%   $263.4188   $263.42   $263.40   $263.40  
  Purchase #6 $85.59   3.400%   $88.5001   $88.50   $88.50   $88.50  
  Purchase #7 $213.33   4.852%   $223.6808   $223.68   $223.70   $223.70  
  7 purchase totals = $1,442.59       $1,543.2581   $1,543.26   $1,543.30   $1,543.20