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 $247.95   11.593%   $276.6948   $276.69   $276.70   $276.70  
  Purchase #2 $191.97   7.743%   $206.8342   $206.83   $206.85   $206.80  
  Purchase #3 $63.47   11.417%   $70.7164   $70.72   $70.70   $70.70  
  Purchase #4 $171.91   7.296%   $184.4526   $184.45   $184.45   $184.50  
  Purchase #5 $11.36   10.309%   $12.5311   $12.53   $12.55   $12.50  
  Purchase #6 $110.83   10.582%   $122.558   $122.56   $122.55   $122.60  
  Purchase #7 $159.42   7.484%   $171.351   $171.35   $171.35   $171.40  
  7 purchase totals = $956.91       $1,045.1381   $1,045.13   $1,045.15   $1,045.20