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 $61.30   9.109%   $66.8838   $66.88   $66.90   $66.90  
  Purchase #2 $180.70   13.650%   $205.3656   $205.37   $205.35   $205.40  
  Purchase #3 $239.43   11.618%   $267.247   $267.25   $267.25   $267.20  
  Purchase #4 $80.33   4.815%   $84.1979   $84.20   $84.20   $84.20  
  Purchase #5 $161.51   13.206%   $182.839   $182.84   $182.85   $182.80  
  Purchase #6 $226.39   6.735%   $241.6374   $241.64   $241.65   $241.60  
  Purchase #7 $219.54   12.770%   $247.5753   $247.58   $247.60   $247.60  
  7 purchase totals = $1,169.20       $1,295.7460   $1,295.76   $1,295.80   $1,295.70