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 $207.62   12.702%   $233.9919   $233.99   $234.00   $234.00  
  Purchase #2 $63.35   9.112%   $69.1225   $69.12   $69.10   $69.10  
  Purchase #3 $74.83   3.496%   $77.4461   $77.45   $77.45   $77.40  
  Purchase #4 $103.26   8.833%   $112.381   $112.38   $112.40   $112.40  
  Purchase #5 $31.41   8.736%   $34.154   $34.15   $34.15   $34.20  
  Purchase #6 $116.80   5.844%   $123.6258   $123.63   $123.65   $123.60  
  Purchase #7 $135.56   6.668%   $144.5991   $144.60   $144.60   $144.60  
  7 purchase totals = $732.83       $795.3204   $795.32   $795.35   $795.30