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 $89.35   6.234%   $94.9201   $94.92   $94.90   $94.90  
  Purchase #2 $214.88   5.513%   $226.7263   $226.73   $226.75   $226.70  
  Purchase #3 $116.65   8.493%   $126.5571   $126.56   $126.55   $126.60  
  Purchase #4 $233.96   4.149%   $243.667   $243.67   $243.65   $243.70  
  Purchase #5 $5.55   13.310%   $6.2887   $6.29   $6.30   $6.30  
  Purchase #6 $62.60   12.626%   $70.5039   $70.50   $70.50   $70.50  
  Purchase #7 $84.25   3.285%   $87.0176   $87.02   $87.00   $87.00  
  7 purchase totals = $807.24       $855.6807   $855.69   $855.65   $855.70