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 $32.63   13.863%   $37.1535   $37.15   $37.15   $37.20  
  Purchase #2 $161.37   3.112%   $166.3918   $166.39   $166.40   $166.40  
  Purchase #3 $212.48   7.623%   $228.6774   $228.68   $228.70   $228.70  
  Purchase #4 $163.65   6.866%   $174.8862   $174.89   $174.90   $174.90  
  Purchase #5 $76.73   6.837%   $81.976   $81.98   $82.00   $82.00  
  Purchase #6 $105.35   4.441%   $110.0286   $110.03   $110.05   $110.00  
  Purchase #7 $150.82   13.543%   $171.2456   $171.25   $171.25   $171.20  
  7 purchase totals = $903.03       $970.3591   $970.37   $970.45   $970.40