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 $228.67   3.437%   $236.5294   $236.53   $236.55   $236.50  
  Purchase #2 $150.36   12.568%   $169.2572   $169.26   $169.25   $169.30  
  Purchase #3 $121.45   11.506%   $135.424   $135.42   $135.40   $135.40  
  Purchase #4 $237.50   6.679%   $253.3626   $253.36   $253.35   $253.40  
  Purchase #5 $161.51   13.780%   $183.7661   $183.77   $183.75   $183.80  
  Purchase #6 $76.68   6.419%   $81.6021   $81.60   $81.60   $81.60  
  Purchase #7 $32.94   4.137%   $34.3027   $34.30   $34.30   $34.30  
  7 purchase totals = $1,009.11       $1,094.2441   $1,094.24   $1,094.20   $1,094.30