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 $62.62   10.782%   $69.3717   $69.37   $69.35   $69.40  
  Purchase #2 $123.85   5.524%   $130.6915   $130.69   $130.70   $130.70  
  Purchase #3 $56.37   7.472%   $60.582   $60.58   $60.60   $60.60  
  Purchase #4 $203.73   13.853%   $231.9527   $231.95   $231.95   $232.00  
  Purchase #5 $180.35   3.530%   $186.7164   $186.72   $186.70   $186.70  
  Purchase #6 $5.27   10.183%   $5.8066   $5.81   $5.80   $5.80  
  Purchase #7 $41.68   9.392%   $45.5946   $45.59   $45.60   $45.60  
  7 purchase totals = $673.87       $730.7155   $730.71   $730.70   $730.80