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 $53.65   6.843%   $57.3213   $57.32   $57.30   $57.30  
  Purchase #2 $114.78   6.719%   $122.4921   $122.49   $122.50   $122.50  
  Purchase #3 $100.71   9.303%   $110.0791   $110.08   $110.10   $110.10  
  Purchase #4 $58.88   3.352%   $60.8537   $60.85   $60.85   $60.90  
  Purchase #5 $239.36   5.293%   $252.0293   $252.03   $252.05   $252.00  
  Purchase #6 $210.90   4.795%   $221.0127   $221.01   $221.00   $221.00  
  Purchase #7 $172.46   5.241%   $181.4986   $181.50   $181.50   $181.50  
  7 purchase totals = $950.74       $1,005.2868   $1,005.28   $1,005.30   $1,005.30