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 $174.96   6.791%   $186.8415   $186.84   $186.85   $186.80  
  Purchase #2 $7.83   11.469%   $8.728   $8.73   $8.75   $8.70  
  Purchase #3 $87.67   3.256%   $90.5245   $90.52   $90.50   $90.50  
  Purchase #4 $35.97   10.620%   $39.79   $39.79   $39.80   $39.80  
  Purchase #5 $203.44   7.806%   $219.3205   $219.32   $219.30   $219.30  
  Purchase #6 $248.31   4.233%   $258.821   $258.82   $258.80   $258.80  
  Purchase #7 $161.60   11.169%   $179.6491   $179.65   $179.65   $179.60  
  7 purchase totals = $919.78       $983.6746   $983.67   $983.65   $983.50