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 $118.94   4.713%   $124.5456   $124.55   $124.55   $124.50  
  Purchase #2 $200.77   12.241%   $225.3463   $225.35   $225.35   $225.30  
  Purchase #3 $57.85   9.146%   $63.141   $63.14   $63.15   $63.10  
  Purchase #4 $31.32   6.359%   $33.3116   $33.31   $33.30   $33.30  
  Purchase #5 $223.48   12.780%   $252.0407   $252.04   $252.05   $252.00  
  Purchase #6 $185.84   6.777%   $198.4344   $198.43   $198.45   $198.40  
  Purchase #7 $93.47   3.797%   $97.0191   $97.02   $97.00   $97.00  
  7 purchase totals = $911.67       $993.8387   $993.84   $993.85   $993.60