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 $88.80   8.256%   $96.1313   $96.13   $96.15   $96.10  
  Purchase #2 $223.49   12.724%   $251.9269   $251.93   $251.95   $251.90  
  Purchase #3 $111.31   9.310%   $121.673   $121.67   $121.65   $121.70  
  Purchase #4 $90.99   8.119%   $98.3775   $98.38   $98.40   $98.40  
  Purchase #5 $106.26   5.666%   $112.2807   $112.28   $112.30   $112.30  
  Purchase #6 $111.76   3.394%   $115.5531   $115.55   $115.55   $115.60  
  Purchase #7 $238.25   3.620%   $246.8747   $246.87   $246.85   $246.90  
  7 purchase totals = $970.86       $1,042.8172   $1,042.81   $1,042.85   $1,042.90