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 $223.32   12.674%   $251.6236   $251.62   $251.60   $251.60  
  Purchase #2 $221.78   4.807%   $232.441   $232.44   $232.45   $232.40  
  Purchase #3 $206.34   13.551%   $234.3011   $234.30   $234.30   $234.30  
  Purchase #4 $85.67   8.444%   $92.904   $92.90   $92.90   $92.90  
  Purchase #5 $219.60   7.867%   $236.8759   $236.88   $236.90   $236.90  
  Purchase #6 $36.37   4.535%   $38.0194   $38.02   $38.00   $38.00  
  Purchase #7 $67.44   11.724%   $75.3467   $75.35   $75.35   $75.30  
  7 purchase totals = $1,060.52       $1,161.5117   $1,161.51   $1,161.50   $1,161.40