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 $155.96   13.179%   $176.514   $176.51   $176.50   $176.50  
  Purchase #2 $71.99   12.764%   $81.1788   $81.18   $81.20   $81.20  
  Purchase #3 $51.72   3.418%   $53.4878   $53.49   $53.50   $53.50  
  Purchase #4 $166.52   12.453%   $187.2567   $187.26   $187.25   $187.30  
  Purchase #5 $207.90   3.433%   $215.0372   $215.04   $215.05   $215.00  
  Purchase #6 $247.98   11.702%   $276.9986   $277.00   $277.00   $277.00  
  Purchase #7 $115.53   6.600%   $123.155   $123.16   $123.15   $123.20  
  7 purchase totals = $1,017.60       $1,113.6281   $1,113.64   $1,113.65   $1,113.70