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 $164.50   12.232%   $184.6216   $184.62   $184.60   $184.60  
  Purchase #2 $200.41   4.783%   $209.9956   $210.00   $210.00   $210.00  
  Purchase #3 $201.32   8.151%   $217.7296   $217.73   $217.75   $217.70  
  Purchase #4 $34.83   11.556%   $38.855   $38.86   $38.85   $38.90  
  Purchase #5 $212.58   6.822%   $227.0822   $227.08   $227.10   $227.10  
  Purchase #6 $82.25   11.585%   $91.7787   $91.78   $91.80   $91.80  
  Purchase #7 $163.84   13.446%   $185.8699   $185.87   $185.85   $185.90  
  7 purchase totals = $1,059.73       $1,155.9326   $1,155.94   $1,155.95   $1,156.00