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 $226.92   8.745%   $246.7642   $246.76   $246.75   $246.80  
  Purchase #2 $59.38   4.863%   $62.2676   $62.27   $62.25   $62.30  
  Purchase #3 $64.59   11.155%   $71.795   $71.80   $71.80   $71.80  
  Purchase #4 $62.62   6.134%   $66.4611   $66.46   $66.45   $66.50  
  Purchase #5 $181.78   11.123%   $201.9994   $202.00   $202.00   $202.00  
  Purchase #6 $109.96   7.209%   $117.887   $117.89   $117.90   $117.90  
  Purchase #7 $200.58   9.404%   $219.4425   $219.44   $219.45   $219.40  
  7 purchase totals = $905.83       $986.6168   $986.62   $986.60   $986.70