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 $26.48   12.365%   $29.7543   $29.75   $29.75   $29.80  
  Purchase #2 $230.95   10.807%   $255.9088   $255.91   $255.90   $255.90  
  Purchase #3 $175.30   6.647%   $186.9522   $186.95   $186.95   $187.00  
  Purchase #4 $226.59   7.552%   $243.7021   $243.70   $243.70   $243.70  
  Purchase #5 $93.39   12.296%   $104.8732   $104.87   $104.85   $104.90  
  Purchase #6 $140.81   9.272%   $153.8659   $153.87   $153.85   $153.90  
  Purchase #7 $61.48   12.749%   $69.3181   $69.32   $69.30   $69.30  
  7 purchase totals = $955.00       $1,044.3746   $1,044.37   $1,044.30   $1,044.50