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 $190.52   6.394%   $202.7018   $202.70   $202.70   $202.70  
  Purchase #2 $241.74   9.684%   $265.1501   $265.15   $265.15   $265.20  
  Purchase #3 $207.34   9.156%   $226.3241   $226.32   $226.30   $226.30  
  Purchase #4 $79.65   5.111%   $83.7209   $83.72   $83.70   $83.70  
  Purchase #5 $34.51   3.349%   $35.6657   $35.67   $35.65   $35.70  
  Purchase #6 $192.89   6.632%   $205.6825   $205.68   $205.70   $205.70  
  Purchase #7 $169.90   13.182%   $192.2962   $192.30   $192.30   $192.30  
  7 purchase totals = $1,116.55       $1,211.5413   $1,211.54   $1,211.50   $1,211.60