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 $56.98   11.245%   $63.3874   $63.39   $63.40   $63.40  
  Purchase #2 $198.52   4.197%   $206.8519   $206.85   $206.85   $206.90  
  Purchase #3 $201.36   13.487%   $228.5174   $228.52   $228.50   $228.50  
  Purchase #4 $86.40   13.288%   $97.8808   $97.88   $97.90   $97.90  
  Purchase #5 $157.83   7.437%   $169.5678   $169.57   $169.55   $169.60  
  Purchase #6 $217.83   8.796%   $236.9903   $236.99   $237.00   $237.00  
  Purchase #7 $52.75   13.141%   $59.6819   $59.68   $59.70   $59.70  
  7 purchase totals = $971.67       $1,062.8775   $1,062.88   $1,062.90   $1,063.00