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 $247.95   6.319%   $263.618   $263.62   $263.60   $263.60  
  Purchase #2 $154.77   5.311%   $162.9898   $162.99   $163.00   $163.00  
  Purchase #3 $26.51   9.648%   $29.0677   $29.07   $29.05   $29.10  
  Purchase #4 $181.98   6.588%   $193.9688   $193.97   $193.95   $194.00  
  Purchase #5 $131.72   5.654%   $139.1674   $139.17   $139.15   $139.20  
  Purchase #6 $163.65   13.514%   $185.7657   $185.77   $185.75   $185.80  
  Purchase #7 $145.90   6.842%   $155.8825   $155.88   $155.90   $155.90  
  7 purchase totals = $1,052.48       $1,130.4599   $1,130.47   $1,130.40   $1,130.60