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 $205.93   10.650%   $227.8615   $227.86   $227.85   $227.90  
  Purchase #2 $181.83   6.254%   $193.2016   $193.20   $193.20   $193.20  
  Purchase #3 $60.31   12.525%   $67.8638   $67.86   $67.85   $67.90  
  Purchase #4 $218.97   9.391%   $239.5335   $239.53   $239.55   $239.50  
  Purchase #5 $92.65   12.532%   $104.2609   $104.26   $104.25   $104.30  
  Purchase #6 $126.27   9.790%   $138.6318   $138.63   $138.65   $138.60  
  Purchase #7 $223.96   4.816%   $234.7459   $234.75   $234.75   $234.70  
  7 purchase totals = $1,109.92       $1,206.0990   $1,206.09   $1,206.10   $1,206.10