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 $55.79   9.301%   $60.979   $60.98   $61.00   $61.00  
  Purchase #2 $246.57   6.558%   $262.7401   $262.74   $262.75   $262.70  
  Purchase #3 $27.71   8.629%   $30.1011   $30.10   $30.10   $30.10  
  Purchase #4 $250.47   11.219%   $278.5702   $278.57   $278.55   $278.60  
  Purchase #5 $36.80   4.472%   $38.4457   $38.45   $38.45   $38.40  
  Purchase #6 $181.39   9.790%   $199.1481   $199.15   $199.15   $199.10  
  Purchase #7 $95.75   12.133%   $107.3673   $107.37   $107.35   $107.40  
  7 purchase totals = $894.48       $977.3515   $977.36   $977.35   $977.30