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 $83.32   12.365%   $93.6225   $93.62   $93.60   $93.60  
  Purchase #2 $247.60   8.461%   $268.5494   $268.55   $268.55   $268.50  
  Purchase #3 $127.58   12.213%   $143.1613   $143.16   $143.15   $143.20  
  Purchase #4 $199.34   13.463%   $226.1771   $226.18   $226.20   $226.20  
  Purchase #5 $134.79   8.193%   $145.8333   $145.83   $145.85   $145.80  
  Purchase #6 $160.99   7.533%   $173.1174   $173.12   $173.10   $173.10  
  Purchase #7 $29.42   13.501%   $33.392   $33.39   $33.40   $33.40  
  7 purchase totals = $983.04       $1,083.8530   $1,083.85   $1,083.85   $1,083.80