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 $201.38   13.290%   $228.1434   $228.14   $228.15   $228.10  
  Purchase #2 $200.77   6.404%   $213.6273   $213.63   $213.65   $213.60  
  Purchase #3 $155.38   8.482%   $168.5593   $168.56   $168.55   $168.60  
  Purchase #4 $246.43   13.465%   $279.6118   $279.61   $279.60   $279.60  
  Purchase #5 $39.33   11.117%   $43.7023   $43.70   $43.70   $43.70  
  Purchase #6 $8.51   13.740%   $9.6793   $9.68   $9.70   $9.70  
  Purchase #7 $107.72   8.305%   $116.6661   $116.67   $116.65   $116.70  
  7 purchase totals = $959.52       $1,059.9895   $1,059.99   $1,060.00   $1,060.00