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 $57.95   6.814%   $61.8987   $61.90   $61.90   $61.90  
  Purchase #2 $203.62   7.591%   $219.0768   $219.08   $219.10   $219.10  
  Purchase #3 $164.34   9.252%   $179.5447   $179.54   $179.55   $179.50  
  Purchase #4 $130.94   5.835%   $138.5803   $138.58   $138.60   $138.60  
  Purchase #5 $143.82   11.456%   $160.296   $160.30   $160.30   $160.30  
  Purchase #6 $183.47   11.872%   $205.2516   $205.25   $205.25   $205.30  
  Purchase #7 $241.95   7.183%   $259.3293   $259.33   $259.35   $259.30  
  7 purchase totals = $1,126.09       $1,223.9774   $1,223.98   $1,224.05   $1,224.00