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 $227.51   8.862%   $247.6719   $247.67   $247.65   $247.70  
  Purchase #2 $109.39   7.737%   $117.8535   $117.85   $117.85   $117.90  
  Purchase #3 $106.52   6.211%   $113.136   $113.14   $113.15   $113.10  
  Purchase #4 $160.66   9.618%   $176.1123   $176.11   $176.10   $176.10  
  Purchase #5 $184.48   3.629%   $191.1748   $191.17   $191.15   $191.20  
  Purchase #6 $247.65   8.855%   $269.5794   $269.58   $269.60   $269.60  
  Purchase #7 $243.75   8.249%   $263.8569   $263.86   $263.85   $263.90  
  7 purchase totals = $1,279.96       $1,379.3848   $1,379.38   $1,379.35   $1,379.50