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 $29.58   7.465%   $31.7881   $31.79   $31.80   $31.80  
  Purchase #2 $80.53   5.723%   $85.1387   $85.14   $85.15   $85.10  
  Purchase #3 $239.80   3.552%   $248.3177   $248.32   $248.30   $248.30  
  Purchase #4 $29.70   10.541%   $32.8307   $32.83   $32.85   $32.80  
  Purchase #5 $165.45   10.213%   $182.3474   $182.35   $182.35   $182.30  
  Purchase #6 $85.73   8.646%   $93.1422   $93.14   $93.15   $93.10  
  Purchase #7 $31.52   13.171%   $35.6715   $35.67   $35.65   $35.70  
  7 purchase totals = $662.31       $709.2363   $709.24   $709.25   $709.10