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 $96.53   5.488%   $101.8276   $101.83   $101.85   $101.80  
  Purchase #2 $67.62   4.563%   $70.7055   $70.71   $70.70   $70.70  
  Purchase #3 $245.25   12.521%   $275.9578   $275.96   $275.95   $276.00  
  Purchase #4 $228.26   12.460%   $256.7012   $256.70   $256.70   $256.70  
  Purchase #5 $71.38   5.514%   $75.3159   $75.32   $75.30   $75.30  
  Purchase #6 $29.90   9.557%   $32.7575   $32.76   $32.75   $32.80  
  Purchase #7 $122.85   3.278%   $126.877   $126.88   $126.90   $126.90  
  7 purchase totals = $861.79       $940.1425   $940.16   $940.15   $940.20