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 $32.86   4.797%   $34.4363   $34.44   $34.45   $34.40  
  Purchase #2 $27.55   5.288%   $29.0068   $29.01   $29.00   $29.00  
  Purchase #3 $127.52   3.558%   $132.0572   $132.06   $132.05   $132.10  
  Purchase #4 $165.67   9.135%   $180.804   $180.80   $180.80   $180.80  
  Purchase #5 $134.95   10.768%   $149.4814   $149.48   $149.50   $149.50  
  Purchase #6 $104.60   3.153%   $107.898   $107.90   $107.90   $107.90  
  Purchase #7 $153.80   5.511%   $162.2759   $162.28   $162.30   $162.30  
  7 purchase totals = $746.95       $795.9596   $795.97   $796.00   $796.00