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 $151.86   7.532%   $163.2981   $163.30   $163.30   $163.30  
  Purchase #2 $246.88   5.662%   $260.8583   $260.86   $260.85   $260.90  
  Purchase #3 $21.58   11.183%   $23.9933   $23.99   $24.00   $24.00  
  Purchase #4 $54.78   4.786%   $57.4018   $57.40   $57.40   $57.40  
  Purchase #5 $207.85   7.517%   $223.4741   $223.47   $223.45   $223.50  
  Purchase #6 $116.74   9.126%   $127.3937   $127.39   $127.40   $127.40  
  Purchase #7 $184.84   8.721%   $200.9599   $200.96   $200.95   $201.00  
  7 purchase totals = $984.53       $1,057.3792   $1,057.37   $1,057.35   $1,057.50