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 $236.42   9.273%   $258.3432   $258.34   $258.35   $258.30  
  Purchase #2 $10.80   5.212%   $11.3629   $11.36   $11.35   $11.40  
  Purchase #3 $41.48   3.294%   $42.8464   $42.85   $42.85   $42.80  
  Purchase #4 $67.66   3.140%   $69.7845   $69.78   $69.80   $69.80  
  Purchase #5 $216.48   4.194%   $225.5592   $225.56   $225.55   $225.60  
  Purchase #6 $34.52   5.449%   $36.401   $36.40   $36.40   $36.40  
  Purchase #7 $138.89   10.121%   $152.9471   $152.95   $152.95   $152.90  
  7 purchase totals = $746.25       $797.2443   $797.24   $797.25   $797.20