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 $22.85   8.104%   $24.7018   $24.70   $24.70   $24.70  
  Purchase #2 $191.58   9.334%   $209.4621   $209.46   $209.45   $209.50  
  Purchase #3 $62.89   8.265%   $68.0879   $68.09   $68.10   $68.10  
  Purchase #4 $169.91   12.391%   $190.9635   $190.96   $190.95   $191.00  
  Purchase #5 $80.99   8.176%   $87.6117   $87.61   $87.60   $87.60  
  Purchase #6 $203.65   11.161%   $226.3794   $226.38   $226.40   $226.40  
  Purchase #7 $220.89   13.756%   $251.2756   $251.28   $251.30   $251.30  
  7 purchase totals = $952.76       $1,058.4820   $1,058.48   $1,058.50   $1,058.60