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 $181.50   10.160%   $199.9404   $199.94   $199.95   $199.90  
  Purchase #2 $56.35   4.707%   $59.0024   $59.00   $59.00   $59.00  
  Purchase #3 $213.47   4.790%   $223.6952   $223.70   $223.70   $223.70  
  Purchase #4 $25.40   13.135%   $28.7363   $28.74   $28.75   $28.70  
  Purchase #5 $165.49   8.866%   $180.1623   $180.16   $180.15   $180.20  
  Purchase #6 $248.57   8.271%   $269.1292   $269.13   $269.15   $269.10  
  Purchase #7 $150.79   8.205%   $163.1623   $163.16   $163.15   $163.20  
  7 purchase totals = $1,041.57       $1,123.8281   $1,123.83   $1,123.85   $1,123.80