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 $180.34   6.721%   $192.4607   $192.46   $192.45   $192.50  
  Purchase #2 $93.67   13.563%   $106.3745   $106.37   $106.35   $106.40  
  Purchase #3 $162.77   4.286%   $169.7463   $169.75   $169.75   $169.70  
  Purchase #4 $224.45   4.245%   $233.9779   $233.98   $234.00   $234.00  
  Purchase #5 $200.78   11.645%   $224.1608   $224.16   $224.15   $224.20  
  Purchase #6 $155.97   5.873%   $165.1301   $165.13   $165.15   $165.10  
  Purchase #7 $128.75   7.542%   $138.4603   $138.46   $138.45   $138.50  
  7 purchase totals = $1,146.73       $1,230.3106   $1,230.31   $1,230.30   $1,230.40