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 $12.50   5.355%   $13.1694   $13.17   $13.15   $13.20  
  Purchase #2 $85.40   13.284%   $96.7445   $96.74   $96.75   $96.70  
  Purchase #3 $149.60   4.819%   $156.8092   $156.81   $156.80   $156.80  
  Purchase #4 $151.58   9.327%   $165.7179   $165.72   $165.70   $165.70  
  Purchase #5 $196.64   4.224%   $204.9461   $204.95   $204.95   $204.90  
  Purchase #6 $241.36   12.578%   $271.7183   $271.72   $271.70   $271.70  
  Purchase #7 $217.95   8.496%   $236.467   $236.47   $236.45   $236.50  
  7 purchase totals = $1,055.03       $1,145.5724   $1,145.58   $1,145.50   $1,145.50