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 $189.97   11.346%   $211.524   $211.52   $211.50   $211.50  
  Purchase #2 $245.36   4.236%   $255.7534   $255.75   $255.75   $255.80  
  Purchase #3 $158.57   6.285%   $168.5361   $168.54   $168.55   $168.50  
  Purchase #4 $173.99   4.260%   $181.402   $181.40   $181.40   $181.40  
  Purchase #5 $45.25   7.275%   $48.5419   $48.54   $48.55   $48.50  
  Purchase #6 $243.93   13.709%   $277.3704   $277.37   $277.35   $277.40  
  Purchase #7 $191.31   5.622%   $202.0654   $202.07   $202.05   $202.10  
  7 purchase totals = $1,248.38       $1,345.1932   $1,345.19   $1,345.15   $1,345.20