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 $246.36   8.361%   $266.9582   $266.96   $266.95   $267.00  
  Purchase #2 $47.93   11.476%   $53.4304   $53.43   $53.45   $53.40  
  Purchase #3 $50.36   12.760%   $56.7859   $56.79   $56.80   $56.80  
  Purchase #4 $78.98   9.856%   $86.7643   $86.76   $86.75   $86.80  
  Purchase #5 $224.83   4.580%   $235.1272   $235.13   $235.15   $235.10  
  Purchase #6 $216.81   12.756%   $244.4663   $244.47   $244.45   $244.50  
  Purchase #7 $165.52   9.250%   $180.8306   $180.83   $180.85   $180.80  
  7 purchase totals = $1,030.79       $1,124.3629   $1,124.37   $1,124.40   $1,124.40