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 $63.80   7.666%   $68.6909   $68.69   $68.70   $68.70  
  Purchase #2 $44.56   11.225%   $49.5619   $49.56   $49.55   $49.60  
  Purchase #3 $116.79   12.470%   $131.3537   $131.35   $131.35   $131.40  
  Purchase #4 $109.33   8.361%   $118.4711   $118.47   $118.45   $118.50  
  Purchase #5 $209.57   11.819%   $234.3391   $234.34   $234.35   $234.30  
  Purchase #6 $218.81   13.146%   $247.5748   $247.57   $247.55   $247.60  
  Purchase #7 $140.47   3.204%   $144.9707   $144.97   $144.95   $145.00  
  7 purchase totals = $903.33       $994.9622   $994.95   $994.90   $995.10