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 $232.94   13.325%   $263.9793   $263.98   $264.00   $264.00  
  Purchase #2 $198.61   9.721%   $217.9169   $217.92   $217.90   $217.90  
  Purchase #3 $172.39   5.345%   $181.6042   $181.60   $181.60   $181.60  
  Purchase #4 $206.86   8.727%   $224.9127   $224.91   $224.90   $224.90  
  Purchase #5 $63.25   5.317%   $66.613   $66.61   $66.60   $66.60  
  Purchase #6 $75.32   10.391%   $83.1465   $83.15   $83.15   $83.10  
  Purchase #7 $101.59   4.402%   $106.062   $106.06   $106.05   $106.10  
  7 purchase totals = $1,050.96       $1,144.2346   $1,144.23   $1,144.20   $1,144.20