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 $170.75   12.454%   $192.0152   $192.02   $192.00   $192.00  
  Purchase #2 $135.66   9.206%   $148.1489   $148.15   $148.15   $148.10  
  Purchase #3 $44.81   13.834%   $51.009   $51.01   $51.00   $51.00  
  Purchase #4 $19.43   5.182%   $20.4369   $20.44   $20.45   $20.40  
  Purchase #5 $106.68   8.465%   $115.7105   $115.71   $115.70   $115.70  
  Purchase #6 $111.52   12.665%   $125.644   $125.64   $125.65   $125.60  
  Purchase #7 $44.33   4.221%   $46.2012   $46.20   $46.20   $46.20  
  7 purchase totals = $633.18       $699.1657   $699.17   $699.15   $699.00