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 $211.88   13.127%   $239.6935   $239.69   $239.70   $239.70  
  Purchase #2 $67.68   13.122%   $76.561   $76.56   $76.55   $76.60  
  Purchase #3 $60.73   4.283%   $63.3311   $63.33   $63.35   $63.30  
  Purchase #4 $198.53   7.298%   $213.0187   $213.02   $213.00   $213.00  
  Purchase #5 $163.52   11.194%   $181.8244   $181.82   $181.80   $181.80  
  Purchase #6 $143.60   4.809%   $150.5057   $150.51   $150.50   $150.50  
  Purchase #7 $168.53   8.181%   $182.3174   $182.32   $182.30   $182.30  
  7 purchase totals = $1,014.47       $1,107.2518   $1,107.25   $1,107.20   $1,107.20