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 $91.83   3.672%   $95.202   $95.20   $95.20   $95.20  
  Purchase #2 $77.90   8.533%   $84.5472   $84.55   $84.55   $84.50  
  Purchase #3 $115.44   9.649%   $126.5788   $126.58   $126.60   $126.60  
  Purchase #4 $223.33   7.285%   $239.5996   $239.60   $239.60   $239.60  
  Purchase #5 $121.38   11.706%   $135.5887   $135.59   $135.60   $135.60  
  Purchase #6 $64.32   7.591%   $69.2025   $69.20   $69.20   $69.20  
  Purchase #7 $146.79   13.163%   $166.112   $166.11   $166.10   $166.10  
  7 purchase totals = $840.99       $916.8308   $916.83   $916.85   $916.80