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 $196.95   3.518%   $203.8787   $203.88   $203.90   $203.90  
  Purchase #2 $48.32   11.691%   $53.9691   $53.97   $53.95   $54.00  
  Purchase #3 $82.94   12.362%   $93.193   $93.19   $93.20   $93.20  
  Purchase #4 $207.28   7.226%   $222.2581   $222.26   $222.25   $222.30  
  Purchase #5 $217.58   11.698%   $243.0325   $243.03   $243.05   $243.00  
  Purchase #6 $133.75   5.497%   $141.1022   $141.10   $141.10   $141.10  
  Purchase #7 $56.85   9.202%   $62.0813   $62.08   $62.10   $62.10  
  7 purchase totals = $943.67       $1,019.5149   $1,019.51   $1,019.55   $1,019.60