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 $8.47   10.804%   $9.3851   $9.39   $9.40   $9.40  
  Purchase #2 $40.55   8.789%   $44.1139   $44.11   $44.10   $44.10  
  Purchase #3 $181.37   13.782%   $206.3664   $206.37   $206.35   $206.40  
  Purchase #4 $97.37   13.431%   $110.4478   $110.45   $110.45   $110.40  
  Purchase #5 $136.69   12.422%   $153.6696   $153.67   $153.65   $153.70  
  Purchase #6 $152.94   7.540%   $164.4717   $164.47   $164.45   $164.50  
  Purchase #7 $204.80   7.453%   $220.0637   $220.06   $220.05   $220.10  
  7 purchase totals = $822.19       $908.5182   $908.52   $908.45   $908.60