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 $10.98   5.741%   $11.6104   $11.61   $11.60   $11.60  
  Purchase #2 $232.65   12.800%   $262.4292   $262.43   $262.45   $262.40  
  Purchase #3 $33.45   6.850%   $35.7413   $35.74   $35.75   $35.70  
  Purchase #4 $27.96   11.591%   $31.2008   $31.20   $31.20   $31.20  
  Purchase #5 $121.74   5.370%   $128.2774   $128.28   $128.30   $128.30  
  Purchase #6 $213.89   11.647%   $238.8018   $238.80   $238.80   $238.80  
  Purchase #7 $248.62   5.355%   $261.9336   $261.93   $261.95   $261.90  
  7 purchase totals = $889.29       $969.9945   $969.99   $970.05   $969.90