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 $56.62   5.204%   $59.5665   $59.57   $59.55   $59.60  
  Purchase #2 $245.52   4.684%   $257.0202   $257.02   $257.00   $257.00  
  Purchase #3 $218.32   4.701%   $228.5832   $228.58   $228.60   $228.60  
  Purchase #4 $136.48   13.419%   $154.7943   $154.79   $154.80   $154.80  
  Purchase #5 $197.97   13.741%   $225.1731   $225.17   $225.15   $225.20  
  Purchase #6 $149.72   5.356%   $157.739   $157.74   $157.75   $157.70  
  Purchase #7 $141.57   9.265%   $154.6865   $154.69   $154.70   $154.70  
  7 purchase totals = $1,146.20       $1,237.5628   $1,237.56   $1,237.55   $1,237.60