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 $218.51   8.247%   $236.5305   $236.53   $236.55   $236.50  
  Purchase #2 $202.25   3.529%   $209.3874   $209.39   $209.40   $209.40  
  Purchase #3 $58.85   9.458%   $64.416   $64.42   $64.40   $64.40  
  Purchase #4 $31.84   9.871%   $34.9829   $34.98   $35.00   $35.00  
  Purchase #5 $12.44   13.441%   $14.1121   $14.11   $14.10   $14.10  
  Purchase #6 $247.28   4.606%   $258.6697   $258.67   $258.65   $258.70  
  Purchase #7 $169.74   5.148%   $178.4782   $178.48   $178.50   $178.50  
  7 purchase totals = $940.91       $996.5768   $996.58   $996.60   $996.60