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 $220.68   6.750%   $235.5759   $235.58   $235.60   $235.60  
  Purchase #2 $104.96   13.572%   $119.2052   $119.21   $119.20   $119.20  
  Purchase #3 $92.26   5.233%   $97.088   $97.09   $97.10   $97.10  
  Purchase #4 $57.36   5.601%   $60.5727   $60.57   $60.55   $60.60  
  Purchase #5 $170.72   5.330%   $179.8194   $179.82   $179.80   $179.80  
  Purchase #6 $111.65   13.365%   $126.572   $126.57   $126.55   $126.60  
  Purchase #7 $226.73   3.205%   $233.9967   $234.00   $234.00   $234.00  
  7 purchase totals = $984.36       $1,052.8299   $1,052.84   $1,052.80   $1,052.90