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 $102.73   13.180%   $116.2698   $116.27   $116.25   $116.30  
  Purchase #2 $151.44   12.705%   $170.6805   $170.68   $170.70   $170.70  
  Purchase #3 $24.31   12.195%   $27.2746   $27.27   $27.25   $27.30  
  Purchase #4 $103.44   12.685%   $116.5614   $116.56   $116.55   $116.60  
  Purchase #5 $235.52   6.379%   $250.5438   $250.54   $250.55   $250.50  
  Purchase #6 $174.39   3.329%   $180.1954   $180.20   $180.20   $180.20  
  Purchase #7 $158.82   8.311%   $172.0195   $172.02   $172.00   $172.00  
  7 purchase totals = $950.65       $1,033.5450   $1,033.54   $1,033.50   $1,033.60