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 $165.82   8.285%   $179.5582   $179.56   $179.55   $179.60  
  Purchase #2 $90.77   5.752%   $95.9911   $95.99   $96.00   $96.00  
  Purchase #3 $65.55   12.652%   $73.8434   $73.84   $73.85   $73.80  
  Purchase #4 $159.56   7.312%   $171.227   $171.23   $171.25   $171.20  
  Purchase #5 $61.88   12.359%   $69.5277   $69.53   $69.55   $69.50  
  Purchase #6 $215.53   3.814%   $223.7503   $223.75   $223.75   $223.80  
  Purchase #7 $187.88   13.109%   $212.5092   $212.51   $212.50   $212.50  
  7 purchase totals = $946.99       $1,026.4069   $1,026.41   $1,026.45   $1,026.40