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 $228.47   10.580%   $252.6421   $252.64   $252.65   $252.60  
  Purchase #2 $88.25   6.686%   $94.1504   $94.15   $94.15   $94.20  
  Purchase #3 $179.77   9.597%   $197.0225   $197.02   $197.00   $197.00  
  Purchase #4 $228.64   7.696%   $246.2361   $246.24   $246.25   $246.20  
  Purchase #5 $24.38   7.519%   $26.2131   $26.21   $26.20   $26.20  
  Purchase #6 $49.50   11.459%   $55.1722   $55.17   $55.15   $55.20  
  Purchase #7 $171.62   7.431%   $184.3731   $184.37   $184.35   $184.40  
  7 purchase totals = $970.63       $1,055.8095   $1,055.80   $1,055.75   $1,055.80