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 $84.86   8.308%   $91.9102   $91.91   $91.90   $91.90  
  Purchase #2 $91.35   8.848%   $99.4326   $99.43   $99.45   $99.40  
  Purchase #3 $222.74   8.464%   $241.5927   $241.59   $241.60   $241.60  
  Purchase #4 $60.64   13.435%   $68.787   $68.79   $68.80   $68.80  
  Purchase #5 $246.69   10.126%   $271.6698   $271.67   $271.65   $271.70  
  Purchase #6 $235.62   9.391%   $257.7471   $257.75   $257.75   $257.70  
  Purchase #7 $154.91   12.506%   $174.283   $174.28   $174.30   $174.30  
  7 purchase totals = $1,096.81       $1,205.4224   $1,205.42   $1,205.45   $1,205.40