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 $198.25   8.328%   $214.7603   $214.76   $214.75   $214.80  
  Purchase #2 $97.58   11.291%   $108.5978   $108.60   $108.60   $108.60  
  Purchase #3 $67.52   6.117%   $71.6502   $71.65   $71.65   $71.70  
  Purchase #4 $209.34   12.847%   $236.2339   $236.23   $236.25   $236.20  
  Purchase #5 $156.47   6.317%   $166.3542   $166.35   $166.35   $166.40  
  Purchase #6 $69.67   11.253%   $77.51   $77.51   $77.50   $77.50  
  Purchase #7 $150.48   5.364%   $158.5517   $158.55   $158.55   $158.60  
  7 purchase totals = $949.31       $1,033.6581   $1,033.65   $1,033.65   $1,033.80