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 $43.39   6.494%   $46.2077   $46.21   $46.20   $46.20  
  Purchase #2 $92.38   13.841%   $105.1663   $105.17   $105.15   $105.20  
  Purchase #3 $186.41   11.102%   $207.1052   $207.11   $207.10   $207.10  
  Purchase #4 $197.68   8.503%   $214.4887   $214.49   $214.50   $214.50  
  Purchase #5 $119.66   5.775%   $126.5704   $126.57   $126.55   $126.60  
  Purchase #6 $154.46   10.402%   $170.5269   $170.53   $170.55   $170.50  
  Purchase #7 $196.90   5.207%   $207.1526   $207.15   $207.15   $207.20  
  7 purchase totals = $990.88       $1,077.2178   $1,077.23   $1,077.20   $1,077.30