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 $67.97   11.631%   $75.8756   $75.88   $75.90   $75.90  
  Purchase #2 $250.62   13.832%   $285.2858   $285.29   $285.30   $285.30  
  Purchase #3 $206.42   7.857%   $222.6384   $222.64   $222.65   $222.60  
  Purchase #4 $216.70   10.612%   $239.6962   $239.70   $239.70   $239.70  
  Purchase #5 $83.89   12.867%   $94.6841   $94.68   $94.70   $94.70  
  Purchase #6 $25.37   10.357%   $27.9976   $28.00   $28.00   $28.00  
  Purchase #7 $62.48   13.473%   $70.8979   $70.90   $70.90   $70.90  
  7 purchase totals = $913.45       $1,017.0756   $1,017.09   $1,017.15   $1,017.10