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 $44.39   7.596%   $47.7619   $47.76   $47.75   $47.80  
  Purchase #2 $150.92   12.178%   $169.299   $169.30   $169.30   $169.30  
  Purchase #3 $208.98   6.381%   $222.315   $222.32   $222.30   $222.30  
  Purchase #4 $109.59   13.368%   $124.24   $124.24   $124.25   $124.20  
  Purchase #5 $108.46   8.183%   $117.3353   $117.34   $117.35   $117.30  
  Purchase #6 $226.88   4.250%   $236.5224   $236.52   $236.50   $236.50  
  Purchase #7 $48.41   11.474%   $53.9646   $53.96   $53.95   $54.00  
  7 purchase totals = $897.63       $971.4382   $971.44   $971.40   $971.40