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 $151.58   11.570%   $169.1178   $169.12   $169.10   $169.10  
  Purchase #2 $175.48   13.610%   $199.3628   $199.36   $199.35   $199.40  
  Purchase #3 $232.98   13.655%   $264.7934   $264.79   $264.80   $264.80  
  Purchase #4 $73.71   7.615%   $79.323   $79.32   $79.30   $79.30  
  Purchase #5 $54.59   9.177%   $59.5997   $59.60   $59.60   $59.60  
  Purchase #6 $219.70   11.513%   $244.9941   $244.99   $245.00   $245.00  
  Purchase #7 $191.77   3.749%   $198.9595   $198.96   $198.95   $199.00  
  7 purchase totals = $1,099.81       $1,216.1503   $1,216.14   $1,216.10   $1,216.20