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 $184.58   12.207%   $207.1117   $207.11   $207.10   $207.10  
  Purchase #2 $131.90   7.421%   $141.6883   $141.69   $141.70   $141.70  
  Purchase #3 $109.35   8.809%   $118.9826   $118.98   $119.00   $119.00  
  Purchase #4 $198.71   9.662%   $217.9094   $217.91   $217.90   $217.90  
  Purchase #5 $98.95   7.128%   $106.0032   $106.00   $106.00   $106.00  
  Purchase #6 $77.72   13.665%   $88.3404   $88.34   $88.35   $88.30  
  Purchase #7 $165.60   8.578%   $179.8052   $179.81   $179.80   $179.80  
  7 purchase totals = $966.81       $1,059.8408   $1,059.84   $1,059.85   $1,059.80