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 $82.77   13.270%   $93.7536   $93.75   $93.75   $93.80  
  Purchase #2 $167.26   3.816%   $173.6426   $173.64   $173.65   $173.60  
  Purchase #3 $219.61   4.521%   $229.5386   $229.54   $229.55   $229.50  
  Purchase #4 $54.72   11.866%   $61.2131   $61.21   $61.20   $61.20  
  Purchase #5 $169.81   4.545%   $177.5279   $177.53   $177.55   $177.50  
  Purchase #6 $41.85   8.336%   $45.3386   $45.34   $45.35   $45.30  
  Purchase #7 $143.45   12.848%   $161.8805   $161.88   $161.90   $161.90  
  7 purchase totals = $879.47       $942.8949   $942.89   $942.95   $942.80