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 $192.69   6.483%   $205.1821   $205.18   $205.20   $205.20  
  Purchase #2 $120.61   10.516%   $133.2933   $133.29   $133.30   $133.30  
  Purchase #3 $175.25   5.403%   $184.7188   $184.72   $184.70   $184.70  
  Purchase #4 $206.66   8.333%   $223.881   $223.88   $223.90   $223.90  
  Purchase #5 $170.29   11.744%   $190.2889   $190.29   $190.30   $190.30  
  Purchase #6 $36.67   3.192%   $37.8405   $37.84   $37.85   $37.80  
  Purchase #7 $34.45   3.817%   $35.765   $35.77   $35.75   $35.80  
  7 purchase totals = $936.62       $1,010.9696   $1,010.97   $1,011.00   $1,011.00