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 $54.59   12.740%   $61.5448   $61.54   $61.55   $61.50  
  Purchase #2 $220.60   3.207%   $227.6746   $227.67   $227.65   $227.70  
  Purchase #3 $87.51   5.858%   $92.6363   $92.64   $92.65   $92.60  
  Purchase #4 $248.53   12.445%   $279.4596   $279.46   $279.45   $279.50  
  Purchase #5 $9.92   5.816%   $10.4969   $10.50   $10.50   $10.50  
  Purchase #6 $115.44   12.671%   $130.0674   $130.07   $130.05   $130.10  
  Purchase #7 $226.29   12.653%   $254.9225   $254.92   $254.90   $254.90  
  7 purchase totals = $962.88       $1,056.8021   $1,056.80   $1,056.75   $1,056.80