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 $192.81   10.272%   $212.6154   $212.62   $212.60   $212.60  
  Purchase #2 $50.72   12.442%   $57.0306   $57.03   $57.05   $57.00  
  Purchase #3 $216.29   6.200%   $229.7   $229.70   $229.70   $229.70  
  Purchase #4 $11.65   13.746%   $13.2514   $13.25   $13.25   $13.30  
  Purchase #5 $57.96   3.481%   $59.9776   $59.98   $60.00   $60.00  
  Purchase #6 $178.57   11.475%   $199.0609   $199.06   $199.05   $199.10  
  Purchase #7 $21.87   10.624%   $24.1935   $24.19   $24.20   $24.20  
  7 purchase totals = $729.87       $795.8294   $795.83   $795.85   $795.90