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 $59.38   10.759%   $65.7687   $65.77   $65.75   $65.80  
  Purchase #2 $238.47   6.568%   $254.1327   $254.13   $254.15   $254.10  
  Purchase #3 $190.92   10.848%   $211.631   $211.63   $211.65   $211.60  
  Purchase #4 $234.61   5.219%   $246.8543   $246.85   $246.85   $246.90  
  Purchase #5 $18.81   13.574%   $21.3633   $21.36   $21.35   $21.40  
  Purchase #6 $58.85   7.794%   $63.4368   $63.44   $63.45   $63.40  
  Purchase #7 $118.55   13.593%   $134.6645   $134.66   $134.65   $134.70  
  7 purchase totals = $919.59       $997.8513   $997.84   $997.85   $997.90