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 $229.62   7.468%   $246.768   $246.77   $246.75   $246.80  
  Purchase #2 $63.76   7.670%   $68.6504   $68.65   $68.65   $68.70  
  Purchase #3 $160.45   4.282%   $167.3205   $167.32   $167.30   $167.30  
  Purchase #4 $130.30   7.482%   $140.049   $140.05   $140.05   $140.00  
  Purchase #5 $156.70   8.287%   $169.6857   $169.69   $169.70   $169.70  
  Purchase #6 $72.73   11.126%   $80.8219   $80.82   $80.80   $80.80  
  Purchase #7 $59.43   7.261%   $63.7452   $63.75   $63.75   $63.70  
  7 purchase totals = $872.99       $937.0407   $937.05   $937.00   $937.00