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 $64.87   3.668%   $67.2494   $67.25   $67.25   $67.20  
  Purchase #2 $91.88   11.510%   $102.4554   $102.46   $102.45   $102.50  
  Purchase #3 $94.60   11.353%   $105.3399   $105.34   $105.35   $105.30  
  Purchase #4 $141.57   7.280%   $151.8763   $151.88   $151.90   $151.90  
  Purchase #5 $44.83   13.298%   $50.7915   $50.79   $50.80   $50.80  
  Purchase #6 $236.28   12.668%   $266.212   $266.21   $266.20   $266.20  
  Purchase #7 $121.65   9.364%   $133.0413   $133.04   $133.05   $133.00  
  7 purchase totals = $795.68       $876.9658   $876.97   $877.00   $876.90