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 $248.43   7.594%   $267.2958   $267.30   $267.30   $267.30  
  Purchase #2 $83.52   3.208%   $86.1993   $86.20   $86.20   $86.20  
  Purchase #3 $115.49   9.267%   $126.1925   $126.19   $126.20   $126.20  
  Purchase #4 $54.42   13.516%   $61.7754   $61.78   $61.80   $61.80  
  Purchase #5 $191.69   4.634%   $200.5729   $200.57   $200.55   $200.60  
  Purchase #6 $234.96   9.796%   $257.9767   $257.98   $258.00   $258.00  
  Purchase #7 $45.66   8.513%   $49.547   $49.55   $49.55   $49.50  
  7 purchase totals = $974.17       $1,049.5596   $1,049.57   $1,049.60   $1,049.60