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 $201.32   3.673%   $208.7145   $208.71   $208.70   $208.70  
  Purchase #2 $230.71   4.107%   $240.1853   $240.19   $240.20   $240.20  
  Purchase #3 $226.54   6.513%   $241.2946   $241.29   $241.30   $241.30  
  Purchase #4 $49.28   5.838%   $52.157   $52.16   $52.15   $52.20  
  Purchase #5 $17.55   5.623%   $18.5368   $18.54   $18.55   $18.50  
  Purchase #6 $210.56   4.790%   $220.6458   $220.65   $220.65   $220.60  
  Purchase #7 $62.27   3.436%   $64.4096   $64.41   $64.40   $64.40  
  7 purchase totals = $998.23       $1,045.9436   $1,045.95   $1,045.95   $1,045.90