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 $245.44   8.313%   $265.8434   $265.84   $265.85   $265.80  
  Purchase #2 $195.51   9.427%   $213.9407   $213.94   $213.95   $213.90  
  Purchase #3 $156.72   5.765%   $165.7549   $165.75   $165.75   $165.80  
  Purchase #4 $222.88   7.635%   $239.8969   $239.90   $239.90   $239.90  
  Purchase #5 $138.90   5.820%   $146.984   $146.98   $147.00   $147.00  
  Purchase #6 $105.29   8.393%   $114.127   $114.13   $114.15   $114.10  
  Purchase #7 $101.58   13.500%   $115.2933   $115.29   $115.30   $115.30  
  7 purchase totals = $1,166.32       $1,261.8402   $1,261.83   $1,261.90   $1,261.80