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 $212.46   13.724%   $241.618   $241.62   $241.60   $241.60  
  Purchase #2 $79.75   9.351%   $87.2074   $87.21   $87.20   $87.20  
  Purchase #3 $170.38   7.158%   $182.5758   $182.58   $182.60   $182.60  
  Purchase #4 $157.75   9.149%   $172.1825   $172.18   $172.20   $172.20  
  Purchase #5 $5.60   5.783%   $5.9238   $5.92   $5.90   $5.90  
  Purchase #6 $84.55   10.673%   $93.574   $93.57   $93.55   $93.60  
  Purchase #7 $63.78   6.560%   $67.964   $67.96   $67.95   $68.00  
  7 purchase totals = $774.27       $851.0455   $851.04   $851.00   $851.10