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 $63.39   7.663%   $68.2476   $68.25   $68.25   $68.20  
  Purchase #2 $108.56   9.248%   $118.5996   $118.60   $118.60   $118.60  
  Purchase #3 $59.45   7.136%   $63.6924   $63.69   $63.70   $63.70  
  Purchase #4 $34.53   8.122%   $37.3345   $37.33   $37.35   $37.30  
  Purchase #5 $232.43   12.141%   $260.6493   $260.65   $260.65   $260.60  
  Purchase #6 $74.33   7.270%   $79.7338   $79.73   $79.75   $79.70  
  Purchase #7 $57.83   11.871%   $64.695   $64.70   $64.70   $64.70  
  7 purchase totals = $630.52       $692.9522   $692.95   $693.00   $692.80