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 $232.57   6.531%   $247.7591   $247.76   $247.75   $247.80  
  Purchase #2 $64.65   6.764%   $69.0229   $69.02   $69.00   $69.00  
  Purchase #3 $53.77   8.699%   $58.4475   $58.45   $58.45   $58.40  
  Purchase #4 $117.27   10.303%   $129.3523   $129.35   $129.35   $129.40  
  Purchase #5 $214.40   10.440%   $236.7834   $236.78   $236.80   $236.80  
  Purchase #6 $167.70   13.789%   $190.8242   $190.82   $190.80   $190.80  
  Purchase #7 $72.86   3.623%   $75.4997   $75.50   $75.50   $75.50  
  7 purchase totals = $923.22       $1,007.6891   $1,007.68   $1,007.65   $1,007.70