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 $55.93   8.467%   $60.6656   $60.67   $60.65   $60.70  
  Purchase #2 $245.97   8.655%   $267.2587   $267.26   $267.25   $267.30  
  Purchase #3 $106.66   7.451%   $114.6072   $114.61   $114.60   $114.60  
  Purchase #4 $207.52   8.826%   $225.8357   $225.84   $225.85   $225.80  
  Purchase #5 $74.92   8.576%   $81.3451   $81.35   $81.35   $81.30  
  Purchase #6 $170.74   8.478%   $185.2153   $185.22   $185.20   $185.20  
  Purchase #7 $29.94   6.277%   $31.8193   $31.82   $31.80   $31.80  
  7 purchase totals = $891.68       $966.7469   $966.77   $966.70   $966.70