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 $200.87   11.343%   $223.6547   $223.65   $223.65   $223.70  
  Purchase #2 $108.65   10.155%   $119.6834   $119.68   $119.70   $119.70  
  Purchase #3 $165.70   5.437%   $174.7091   $174.71   $174.70   $174.70  
  Purchase #4 $244.69   9.632%   $268.2585   $268.26   $268.25   $268.30  
  Purchase #5 $187.80   5.551%   $198.2248   $198.22   $198.20   $198.20  
  Purchase #6 $63.86   7.177%   $68.4432   $68.44   $68.45   $68.40  
  Purchase #7 $177.65   13.616%   $201.8388   $201.84   $201.85   $201.80  
  7 purchase totals = $1,149.22       $1,254.8125   $1,254.80   $1,254.80   $1,254.80