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 $144.34   13.470%   $163.7826   $163.78   $163.80   $163.80  
  Purchase #2 $149.88   11.200%   $166.6666   $166.67   $166.65   $166.70  
  Purchase #3 $235.56   9.108%   $257.0148   $257.01   $257.00   $257.00  
  Purchase #4 $112.25   8.374%   $121.6498   $121.65   $121.65   $121.60  
  Purchase #5 $250.80   10.315%   $276.67   $276.67   $276.65   $276.70  
  Purchase #6 $245.59   8.592%   $266.6911   $266.69   $266.70   $266.70  
  Purchase #7 $12.77   11.177%   $14.1973   $14.20   $14.20   $14.20  
  7 purchase totals = $1,151.19       $1,266.6722   $1,266.67   $1,266.65   $1,266.70