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 $27.53   7.214%   $29.516   $29.52   $29.50   $29.50  
  Purchase #2 $49.90   4.706%   $52.2483   $52.25   $52.25   $52.20  
  Purchase #3 $50.93   10.392%   $56.2226   $56.22   $56.20   $56.20  
  Purchase #4 $207.36   6.711%   $221.2759   $221.28   $221.30   $221.30  
  Purchase #5 $200.90   11.277%   $223.5555   $223.56   $223.55   $223.60  
  Purchase #6 $232.66   7.212%   $249.4394   $249.44   $249.45   $249.40  
  Purchase #7 $175.94   3.353%   $181.8393   $181.84   $181.85   $181.80  
  7 purchase totals = $945.22       $1,014.0970   $1,014.11   $1,014.10   $1,014.00