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 $242.55   8.277%   $262.6259   $262.63   $262.65   $262.60  
  Purchase #2 $242.74   4.495%   $253.6512   $253.65   $253.65   $253.70  
  Purchase #3 $77.80   8.547%   $84.4496   $84.45   $84.45   $84.40  
  Purchase #4 $187.96   7.294%   $201.6698   $201.67   $201.65   $201.70  
  Purchase #5 $183.43   4.660%   $191.9778   $191.98   $192.00   $192.00  
  Purchase #6 $31.67   13.390%   $35.9106   $35.91   $35.90   $35.90  
  Purchase #7 $50.52   5.148%   $53.1208   $53.12   $53.10   $53.10  
  7 purchase totals = $1,016.67       $1,083.4057   $1,083.41   $1,083.40   $1,083.40