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 $30.61   6.466%   $32.5892   $32.59   $32.60   $32.60  
  Purchase #2 $214.35   7.360%   $230.1262   $230.13   $230.15   $230.10  
  Purchase #3 $187.59   5.807%   $198.4834   $198.48   $198.50   $198.50  
  Purchase #4 $214.41   11.830%   $239.7747   $239.77   $239.75   $239.80  
  Purchase #5 $176.70   10.836%   $195.8472   $195.85   $195.85   $195.80  
  Purchase #6 $22.97   6.752%   $24.5209   $24.52   $24.50   $24.50  
  Purchase #7 $94.58   4.226%   $98.577   $98.58   $98.60   $98.60  
  7 purchase totals = $941.21       $1,019.9186   $1,019.92   $1,019.95   $1,019.90