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 $204.66   13.806%   $232.9154   $232.92   $232.90   $232.90  
  Purchase #2 $192.29   3.254%   $198.5471   $198.55   $198.55   $198.50  
  Purchase #3 $202.52   11.434%   $225.6761   $225.68   $225.70   $225.70  
  Purchase #4 $58.65   9.537%   $64.2435   $64.24   $64.25   $64.20  
  Purchase #5 $102.90   3.355%   $106.3523   $106.35   $106.35   $106.40  
  Purchase #6 $100.37   13.532%   $113.9521   $113.95   $113.95   $114.00  
  Purchase #7 $225.92   7.857%   $243.6705   $243.67   $243.65   $243.70  
  7 purchase totals = $1,087.31       $1,185.3570   $1,185.36   $1,185.35   $1,185.40