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 $60.46   12.697%   $68.1366   $68.14   $68.15   $68.10  
  Purchase #2 $17.88   4.313%   $18.6512   $18.65   $18.65   $18.70  
  Purchase #3 $247.46   11.545%   $276.0293   $276.03   $276.05   $276.00  
  Purchase #4 $176.82   10.865%   $196.0315   $196.03   $196.05   $196.00  
  Purchase #5 $222.90   3.107%   $229.8255   $229.83   $229.85   $229.80  
  Purchase #6 $220.76   9.323%   $241.3415   $241.34   $241.35   $241.30  
  Purchase #7 $147.96   10.536%   $163.5491   $163.55   $163.55   $163.50  
  7 purchase totals = $1,094.24       $1,193.5647   $1,193.57   $1,193.65   $1,193.40