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 $97.60   10.302%   $107.6548   $107.65   $107.65   $107.70  
  Purchase #2 $211.79   6.233%   $224.9909   $224.99   $225.00   $225.00  
  Purchase #3 $42.54   7.861%   $45.8841   $45.88   $45.90   $45.90  
  Purchase #4 $66.99   9.461%   $73.3279   $73.33   $73.35   $73.30  
  Purchase #5 $240.71   9.366%   $263.2549   $263.25   $263.25   $263.30  
  Purchase #6 $60.32   6.210%   $64.0659   $64.07   $64.05   $64.10  
  Purchase #7 $110.67   12.369%   $124.3588   $124.36   $124.35   $124.40  
  7 purchase totals = $830.62       $903.5373   $903.53   $903.55   $903.70