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 $235.94   13.201%   $267.0864   $267.09   $267.10   $267.10  
  Purchase #2 $189.76   4.666%   $198.6142   $198.61   $198.60   $198.60  
  Purchase #3 $28.52   3.746%   $29.5884   $29.59   $29.60   $29.60  
  Purchase #4 $228.51   11.265%   $254.2517   $254.25   $254.25   $254.30  
  Purchase #5 $216.92   10.267%   $239.1912   $239.19   $239.20   $239.20  
  Purchase #6 $204.25   10.446%   $225.586   $225.59   $225.60   $225.60  
  Purchase #7 $41.63   9.120%   $45.4267   $45.43   $45.45   $45.40  
  7 purchase totals = $1,145.53       $1,259.7446   $1,259.75   $1,259.80   $1,259.80