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 $185.61   8.803%   $201.9492   $201.95   $201.95   $201.90  
  Purchase #2 $34.98   6.291%   $37.1806   $37.18   $37.20   $37.20  
  Purchase #3 $203.53   6.189%   $216.1265   $216.13   $216.15   $216.10  
  Purchase #4 $227.28   4.283%   $237.0144   $237.01   $237.00   $237.00  
  Purchase #5 $115.58   4.159%   $120.387   $120.39   $120.40   $120.40  
  Purchase #6 $57.84   5.792%   $61.1901   $61.19   $61.20   $61.20  
  Purchase #7 $49.44   11.523%   $55.137   $55.14   $55.15   $55.10  
  7 purchase totals = $874.26       $928.9848   $928.99   $929.05   $928.90