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 $248.30   7.757%   $267.5606   $267.56   $267.55   $267.60  
  Purchase #2 $150.92   5.374%   $159.0304   $159.03   $159.05   $159.00  
  Purchase #3 $221.29   7.356%   $237.5681   $237.57   $237.55   $237.60  
  Purchase #4 $106.65   10.757%   $118.1223   $118.12   $118.10   $118.10  
  Purchase #5 $240.74   12.787%   $271.5234   $271.52   $271.50   $271.50  
  Purchase #6 $115.68   4.218%   $120.5594   $120.56   $120.55   $120.60  
  Purchase #7 $237.40   6.365%   $252.5105   $252.51   $252.50   $252.50  
  7 purchase totals = $1,320.98       $1,426.8747   $1,426.87   $1,426.80   $1,426.90