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 $54.37   10.586%   $60.1256   $60.13   $60.15   $60.10  
  Purchase #2 $202.78   9.797%   $222.6464   $222.65   $222.65   $222.60  
  Purchase #3 $120.52   4.369%   $125.7855   $125.79   $125.80   $125.80  
  Purchase #4 $151.78   13.118%   $171.6905   $171.69   $171.70   $171.70  
  Purchase #5 $229.81   4.606%   $240.395   $240.40   $240.40   $240.40  
  Purchase #6 $104.81   7.476%   $112.6456   $112.65   $112.65   $112.60  
  Purchase #7 $61.74   8.663%   $67.0885   $67.09   $67.10   $67.10  
  7 purchase totals = $925.81       $1,000.3771   $1,000.40   $1,000.45   $1,000.30