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 $93.65   13.410%   $106.2085   $106.21   $106.20   $106.20  
  Purchase #2 $49.56   5.615%   $52.3428   $52.34   $52.35   $52.30  
  Purchase #3 $199.81   13.352%   $226.4886   $226.49   $226.50   $226.50  
  Purchase #4 $211.88   10.246%   $233.5892   $233.59   $233.60   $233.60  
  Purchase #5 $60.67   10.199%   $66.8577   $66.86   $66.85   $66.90  
  Purchase #6 $153.87   10.383%   $169.8463   $169.85   $169.85   $169.80  
  Purchase #7 $140.93   8.407%   $152.778   $152.78   $152.80   $152.80  
  7 purchase totals = $910.37       $1,008.1111   $1,008.12   $1,008.15   $1,008.10