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 $232.93   13.551%   $264.4943   $264.49   $264.50   $264.50  
  Purchase #2 $172.77   12.494%   $194.3559   $194.36   $194.35   $194.40  
  Purchase #3 $63.28   8.564%   $68.6993   $68.70   $68.70   $68.70  
  Purchase #4 $37.25   11.142%   $41.4004   $41.40   $41.40   $41.40  
  Purchase #5 $30.98   12.533%   $34.8627   $34.86   $34.85   $34.90  
  Purchase #6 $241.97   11.711%   $270.3071   $270.31   $270.30   $270.30  
  Purchase #7 $245.29   8.227%   $265.47   $265.47   $265.45   $265.50  
  7 purchase totals = $1,024.47       $1,139.5897   $1,139.59   $1,139.55   $1,139.70