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 $238.55   8.654%   $259.1941   $259.19   $259.20   $259.20  
  Purchase #2 $204.98   8.287%   $221.9667   $221.97   $221.95   $222.00  
  Purchase #3 $122.25   6.749%   $130.5007   $130.50   $130.50   $130.50  
  Purchase #4 $248.51   8.500%   $269.6334   $269.63   $269.65   $269.60  
  Purchase #5 $87.27   9.367%   $95.4446   $95.44   $95.45   $95.40  
  Purchase #6 $179.64   12.244%   $201.6351   $201.64   $201.65   $201.60  
  Purchase #7 $191.91   7.832%   $206.9404   $206.94   $206.95   $206.90  
  7 purchase totals = $1,273.11       $1,385.3150   $1,385.31   $1,385.35   $1,385.20