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 $90.96   6.227%   $96.6241   $96.62   $96.60   $96.60  
  Purchase #2 $107.46   4.837%   $112.6578   $112.66   $112.65   $112.70  
  Purchase #3 $188.29   8.195%   $203.7204   $203.72   $203.70   $203.70  
  Purchase #4 $246.95   10.183%   $272.0969   $272.10   $272.10   $272.10  
  Purchase #5 $34.74   11.209%   $38.634   $38.63   $38.65   $38.60  
  Purchase #6 $167.74   9.359%   $183.4388   $183.44   $183.45   $183.40  
  Purchase #7 $10.72   3.810%   $11.1284   $11.13   $11.15   $11.10  
  7 purchase totals = $846.86       $918.3004   $918.30   $918.30   $918.20