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 $76.53   5.387%   $80.6527   $80.65   $80.65   $80.70  
  Purchase #2 $206.81   13.490%   $234.7087   $234.71   $234.70   $234.70  
  Purchase #3 $205.58   3.128%   $212.0105   $212.01   $212.00   $212.00  
  Purchase #4 $51.84   10.828%   $57.4532   $57.45   $57.45   $57.50  
  Purchase #5 $191.62   11.811%   $214.2522   $214.25   $214.25   $214.30  
  Purchase #6 $243.98   6.484%   $259.7997   $259.80   $259.80   $259.80  
  Purchase #7 $106.39   3.470%   $110.0817   $110.08   $110.10   $110.10  
  7 purchase totals = $1,082.75       $1,168.9587   $1,168.95   $1,168.95   $1,169.10