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 $62.99   8.569%   $68.3876   $68.39   $68.40   $68.40  
  Purchase #2 $220.45   6.870%   $235.5949   $235.59   $235.60   $235.60  
  Purchase #3 $27.27   6.295%   $28.9866   $28.99   $29.00   $29.00  
  Purchase #4 $250.85   9.650%   $275.057   $275.06   $275.05   $275.10  
  Purchase #5 $85.50   9.496%   $93.6191   $93.62   $93.60   $93.60  
  Purchase #6 $75.30   7.552%   $80.9867   $80.99   $81.00   $81.00  
  Purchase #7 $83.78   5.242%   $88.1717   $88.17   $88.15   $88.20  
  7 purchase totals = $806.14       $870.8036   $870.81   $870.80   $870.90