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 $233.45   7.856%   $251.7898   $251.79   $251.80   $251.80  
  Purchase #2 $62.42   10.521%   $68.9872   $68.99   $69.00   $69.00  
  Purchase #3 $145.85   5.782%   $154.283   $154.28   $154.30   $154.30  
  Purchase #4 $73.71   10.456%   $81.4171   $81.42   $81.40   $81.40  
  Purchase #5 $172.89   3.214%   $178.4467   $178.45   $178.45   $178.40  
  Purchase #6 $99.61   13.803%   $113.3592   $113.36   $113.35   $113.40  
  Purchase #7 $184.42   13.818%   $209.9032   $209.90   $209.90   $209.90  
  7 purchase totals = $972.35       $1,058.1862   $1,058.19   $1,058.20   $1,058.20