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 $56.50   12.453%   $63.5359   $63.54   $63.55   $63.50  
  Purchase #2 $169.54   13.223%   $191.9583   $191.96   $191.95   $192.00  
  Purchase #3 $84.63   13.864%   $96.3631   $96.36   $96.35   $96.40  
  Purchase #4 $18.80   6.424%   $20.0077   $20.01   $20.00   $20.00  
  Purchase #5 $22.65   7.565%   $24.3635   $24.36   $24.35   $24.40  
  Purchase #6 $133.48   4.570%   $139.58   $139.58   $139.60   $139.60  
  Purchase #7 $38.35   9.288%   $41.9119   $41.91   $41.90   $41.90  
  7 purchase totals = $523.95       $577.7204   $577.72   $577.70   $577.80