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 $69.28   11.262%   $77.0823   $77.08   $77.10   $77.10  
  Purchase #2 $234.86   3.598%   $243.3103   $243.31   $243.30   $243.30  
  Purchase #3 $101.59   8.835%   $110.5655   $110.57   $110.55   $110.60  
  Purchase #4 $93.64   8.607%   $101.6996   $101.70   $101.70   $101.70  
  Purchase #5 $6.36   10.724%   $7.042   $7.04   $7.05   $7.00  
  Purchase #6 $160.65   9.808%   $176.4066   $176.41   $176.40   $176.40  
  Purchase #7 $66.43   12.764%   $74.9091   $74.91   $74.90   $74.90  
  7 purchase totals = $732.81       $791.0154   $791.02   $791.00   $791.00