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 $46.74   13.637%   $53.1139   $53.11   $53.10   $53.10  
  Purchase #2 $174.59   6.767%   $186.4045   $186.40   $186.40   $186.40  
  Purchase #3 $87.88   4.691%   $92.0025   $92.00   $92.00   $92.00  
  Purchase #4 $63.89   6.170%   $67.832   $67.83   $67.85   $67.80  
  Purchase #5 $51.93   13.646%   $59.0164   $59.02   $59.00   $59.00  
  Purchase #6 $74.91   9.379%   $81.9358   $81.94   $81.95   $81.90  
  Purchase #7 $23.52   13.754%   $26.7549   $26.75   $26.75   $26.80  
  7 purchase totals = $523.46       $567.0600   $567.05   $567.05   $567.00