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 $245.27   5.182%   $257.9799   $257.98   $258.00   $258.00  
  Purchase #2 $131.74   5.106%   $138.4666   $138.47   $138.45   $138.50  
  Purchase #3 $165.89   11.233%   $184.5244   $184.52   $184.50   $184.50  
  Purchase #4 $240.91   10.797%   $266.9211   $266.92   $266.90   $266.90  
  Purchase #5 $219.99   10.259%   $242.5588   $242.56   $242.55   $242.60  
  Purchase #6 $249.79   5.850%   $264.4027   $264.40   $264.40   $264.40  
  Purchase #7 $90.85   4.564%   $94.9964   $95.00   $95.00   $95.00  
  7 purchase totals = $1,344.44       $1,449.8499   $1,449.85   $1,449.80   $1,449.90