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 $208.66   13.755%   $237.3612   $237.36   $237.35   $237.40  
  Purchase #2 $96.67   5.481%   $101.9685   $101.97   $101.95   $102.00  
  Purchase #3 $154.34   7.461%   $165.8553   $165.86   $165.85   $165.90  
  Purchase #4 $177.57   10.673%   $196.522   $196.52   $196.50   $196.50  
  Purchase #5 $240.29   7.165%   $257.5068   $257.51   $257.50   $257.50  
  Purchase #6 $184.37   4.162%   $192.0435   $192.04   $192.05   $192.00  
  Purchase #7 $113.62   8.512%   $123.2913   $123.29   $123.30   $123.30  
  7 purchase totals = $1,175.52       $1,274.5486   $1,274.55   $1,274.50   $1,274.60