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 $79.82   5.626%   $84.3107   $84.31   $84.30   $84.30  
  Purchase #2 $196.27   5.591%   $207.2435   $207.24   $207.25   $207.20  
  Purchase #3 $223.32   4.311%   $232.9473   $232.95   $232.95   $232.90  
  Purchase #4 $203.51   11.184%   $226.2706   $226.27   $226.25   $226.30  
  Purchase #5 $213.56   4.839%   $223.8942   $223.89   $223.90   $223.90  
  Purchase #6 $168.67   12.255%   $189.3405   $189.34   $189.35   $189.30  
  Purchase #7 $150.40   7.677%   $161.9462   $161.95   $161.95   $161.90  
  7 purchase totals = $1,235.55       $1,325.9530   $1,325.95   $1,325.95   $1,325.80