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 $189.93   5.464%   $200.3078   $200.31   $200.30   $200.30  
  Purchase #2 $241.92   3.424%   $250.2033   $250.20   $250.20   $250.20  
  Purchase #3 $84.43   8.599%   $91.6901   $91.69   $91.70   $91.70  
  Purchase #4 $236.92   13.829%   $269.6837   $269.68   $269.70   $269.70  
  Purchase #5 $56.84   12.626%   $64.0166   $64.02   $64.00   $64.00  
  Purchase #6 $233.50   3.353%   $241.3293   $241.33   $241.35   $241.30  
  Purchase #7 $154.99   8.824%   $168.6663   $168.67   $168.65   $168.70  
  7 purchase totals = $1,198.53       $1,285.8971   $1,285.90   $1,285.90   $1,285.90