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 $85.31   11.141%   $94.8144   $94.81   $94.80   $94.80  
  Purchase #2 $210.89   13.637%   $239.6491   $239.65   $239.65   $239.60  
  Purchase #3 $43.96   11.861%   $49.1741   $49.17   $49.15   $49.20  
  Purchase #4 $244.52   10.268%   $269.6273   $269.63   $269.65   $269.60  
  Purchase #5 $208.54   7.393%   $223.9574   $223.96   $223.95   $224.00  
  Purchase #6 $224.35   3.319%   $231.7962   $231.80   $231.80   $231.80  
  Purchase #7 $215.92   4.367%   $225.3492   $225.35   $225.35   $225.30  
  7 purchase totals = $1,233.49       $1,334.3677   $1,334.37   $1,334.35   $1,334.30