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 $35.98   5.556%   $37.979   $37.98   $38.00   $38.00  
  Purchase #2 $211.56   3.526%   $219.0196   $219.02   $219.00   $219.00  
  Purchase #3 $38.44   11.348%   $42.8022   $42.80   $42.80   $42.80  
  Purchase #4 $197.53   7.207%   $211.766   $211.77   $211.75   $211.80  
  Purchase #5 $87.93   5.466%   $92.7363   $92.74   $92.75   $92.70  
  Purchase #6 $239.44   12.678%   $269.7962   $269.80   $269.80   $269.80  
  Purchase #7 $58.39   8.874%   $63.5715   $63.57   $63.55   $63.60  
  7 purchase totals = $869.27       $937.6708   $937.68   $937.65   $937.70