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 $57.67   6.607%   $61.4803   $61.48   $61.50   $61.50  
  Purchase #2 $246.74   8.468%   $267.6339   $267.63   $267.65   $267.60  
  Purchase #3 $241.31   8.210%   $261.1216   $261.12   $261.10   $261.10  
  Purchase #4 $118.56   13.494%   $134.5585   $134.56   $134.55   $134.60  
  Purchase #5 $9.61   11.873%   $10.751   $10.75   $10.75   $10.80  
  Purchase #6 $147.79   6.704%   $157.6978   $157.70   $157.70   $157.70  
  Purchase #7 $143.51   8.555%   $155.7873   $155.79   $155.80   $155.80  
  7 purchase totals = $965.19       $1,049.0304   $1,049.03   $1,049.05   $1,049.10