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 $52.80   11.632%   $58.9417   $58.94   $58.95   $58.90  
  Purchase #2 $148.48   5.490%   $156.6316   $156.63   $156.65   $156.60  
  Purchase #3 $209.51   7.341%   $224.8901   $224.89   $224.90   $224.90  
  Purchase #4 $171.79   7.547%   $184.755   $184.76   $184.75   $184.80  
  Purchase #5 $103.42   11.464%   $115.2761   $115.28   $115.30   $115.30  
  Purchase #6 $156.37   12.825%   $176.4245   $176.42   $176.40   $176.40  
  Purchase #7 $202.43   12.774%   $228.2884   $228.29   $228.30   $228.30  
  7 purchase totals = $1,044.80       $1,145.2074   $1,145.21   $1,145.25   $1,145.20