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 $62.56   13.421%   $70.9562   $70.96   $70.95   $71.00  
  Purchase #2 $163.74   7.419%   $175.8879   $175.89   $175.90   $175.90  
  Purchase #3 $172.37   4.388%   $179.9336   $179.93   $179.95   $179.90  
  Purchase #4 $55.68   13.354%   $63.1155   $63.12   $63.10   $63.10  
  Purchase #5 $107.31   6.186%   $113.9482   $113.95   $113.95   $113.90  
  Purchase #6 $250.80   8.443%   $271.975   $271.98   $272.00   $272.00  
  Purchase #7 $223.39   3.424%   $231.0389   $231.04   $231.05   $231.00  
  7 purchase totals = $1,035.85       $1,106.8553   $1,106.87   $1,106.90   $1,106.80