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 $177.41   11.243%   $197.3562   $197.36   $197.35   $197.40  
  Purchase #2 $73.87   13.669%   $83.9673   $83.97   $83.95   $84.00  
  Purchase #3 $162.59   12.476%   $182.8747   $182.87   $182.85   $182.90  
  Purchase #4 $188.68   12.517%   $212.2971   $212.30   $212.30   $212.30  
  Purchase #5 $87.78   4.848%   $92.0356   $92.04   $92.05   $92.00  
  Purchase #6 $203.81   10.681%   $225.5789   $225.58   $225.60   $225.60  
  Purchase #7 $51.55   10.161%   $56.788   $56.79   $56.80   $56.80  
  7 purchase totals = $945.69       $1,050.8978   $1,050.91   $1,050.90   $1,051.00