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 $46.47   6.608%   $49.5407   $49.54   $49.55   $49.50  
  Purchase #2 $186.33   4.797%   $195.2683   $195.27   $195.25   $195.30  
  Purchase #3 $170.48   4.216%   $177.6674   $177.67   $177.65   $177.70  
  Purchase #4 $201.65   12.476%   $226.8079   $226.81   $226.80   $226.80  
  Purchase #5 $170.53   9.114%   $186.0721   $186.07   $186.05   $186.10  
  Purchase #6 $67.25   11.196%   $74.7793   $74.78   $74.80   $74.80  
  Purchase #7 $89.38   13.809%   $101.7225   $101.72   $101.70   $101.70  
  7 purchase totals = $932.09       $1,011.8582   $1,011.86   $1,011.80   $1,011.90