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 $211.75   11.422%   $235.9361   $235.94   $235.95   $235.90  
  Purchase #2 $115.32   13.142%   $130.4754   $130.48   $130.50   $130.50  
  Purchase #3 $93.53   3.625%   $96.9205   $96.92   $96.90   $96.90  
  Purchase #4 $83.76   4.751%   $87.7394   $87.74   $87.75   $87.70  
  Purchase #5 $124.94   10.207%   $137.6926   $137.69   $137.70   $137.70  
  Purchase #6 $180.75   3.431%   $186.9515   $186.95   $186.95   $187.00  
  Purchase #7 $118.94   6.239%   $126.3607   $126.36   $126.35   $126.40  
  7 purchase totals = $928.99       $1,002.0762   $1,002.08   $1,002.10   $1,002.10