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 $202.99   10.740%   $224.7911   $224.79   $224.80   $224.80  
  Purchase #2 $147.94   3.656%   $153.3487   $153.35   $153.35   $153.30  
  Purchase #3 $247.27   3.588%   $256.142   $256.14   $256.15   $256.10  
  Purchase #4 $212.32   7.685%   $228.6368   $228.64   $228.65   $228.60  
  Purchase #5 $140.75   13.620%   $159.9202   $159.92   $159.90   $159.90  
  Purchase #6 $209.96   9.674%   $230.2715   $230.27   $230.25   $230.30  
  Purchase #7 $21.55   13.368%   $24.4308   $24.43   $24.45   $24.40  
  7 purchase totals = $1,182.78       $1,277.5411   $1,277.54   $1,277.55   $1,277.40