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 $68.36   9.724%   $75.0073   $75.01   $75.00   $75.00  
  Purchase #2 $215.85   13.521%   $245.0351   $245.04   $245.05   $245.00  
  Purchase #3 $25.71   5.771%   $27.1937   $27.19   $27.20   $27.20  
  Purchase #4 $173.26   6.415%   $184.3746   $184.37   $184.35   $184.40  
  Purchase #5 $34.34   10.393%   $37.909   $37.91   $37.90   $37.90  
  Purchase #6 $121.35   6.634%   $129.4004   $129.40   $129.40   $129.40  
  Purchase #7 $44.87   8.246%   $48.57   $48.57   $48.55   $48.60  
  7 purchase totals = $683.74       $747.4901   $747.49   $747.45   $747.50