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 $48.52   11.270%   $53.9882   $53.99   $54.00   $54.00  
  Purchase #2 $190.94   9.626%   $209.3199   $209.32   $209.30   $209.30  
  Purchase #3 $95.73   11.123%   $106.378   $106.38   $106.40   $106.40  
  Purchase #4 $141.93   7.786%   $152.9807   $152.98   $153.00   $153.00  
  Purchase #5 $178.94   7.645%   $192.62   $192.62   $192.60   $192.60  
  Purchase #6 $212.48   10.339%   $234.4483   $234.45   $234.45   $234.40  
  Purchase #7 $61.27   13.417%   $69.4906   $69.49   $69.50   $69.50  
  7 purchase totals = $929.81       $1,019.2257   $1,019.23   $1,019.25   $1,019.20