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 $108.56   9.328%   $118.6865   $118.69   $118.70   $118.70  
  Purchase #2 $159.60   13.364%   $180.9289   $180.93   $180.95   $180.90  
  Purchase #3 $156.51   12.643%   $176.2976   $176.30   $176.30   $176.30  
  Purchase #4 $231.65   9.415%   $253.4598   $253.46   $253.45   $253.50  
  Purchase #5 $244.55   8.581%   $265.5348   $265.53   $265.55   $265.50  
  Purchase #6 $249.59   6.411%   $265.5912   $265.59   $265.60   $265.60  
  Purchase #7 $226.52   3.327%   $234.0563   $234.06   $234.05   $234.10  
  7 purchase totals = $1,376.98       $1,494.5551   $1,494.56   $1,494.60   $1,494.60