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 $41.45   5.657%   $43.7948   $43.79   $43.80   $43.80  
  Purchase #2 $11.55   13.167%   $13.0708   $13.07   $13.05   $13.10  
  Purchase #3 $198.96   4.365%   $207.6446   $207.64   $207.65   $207.60  
  Purchase #4 $69.81   8.519%   $75.7571   $75.76   $75.75   $75.80  
  Purchase #5 $99.64   3.671%   $103.2978   $103.30   $103.30   $103.30  
  Purchase #6 $151.35   6.142%   $160.6459   $160.65   $160.65   $160.60  
  Purchase #7 $235.61   5.372%   $248.267   $248.27   $248.25   $248.30  
  7 purchase totals = $808.37       $852.4780   $852.48   $852.45   $852.50