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 $184.60   9.108%   $201.4134   $201.41   $201.40   $201.40  
  Purchase #2 $223.91   10.650%   $247.7564   $247.76   $247.75   $247.80  
  Purchase #3 $237.53   4.612%   $248.4849   $248.48   $248.50   $248.50  
  Purchase #4 $92.35   5.826%   $97.7303   $97.73   $97.75   $97.70  
  Purchase #5 $57.93   11.250%   $64.4471   $64.45   $64.45   $64.40  
  Purchase #6 $10.37   12.716%   $11.6886   $11.69   $11.70   $11.70  
  Purchase #7 $23.39   4.372%   $24.4126   $24.41   $24.40   $24.40  
  7 purchase totals = $830.08       $895.9333   $895.93   $895.95   $895.90