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 $54.69   12.571%   $61.5651   $61.57   $61.55   $61.60  
  Purchase #2 $224.31   12.521%   $252.3959   $252.40   $252.40   $252.40  
  Purchase #3 $139.77   4.128%   $145.5397   $145.54   $145.55   $145.50  
  Purchase #4 $243.82   5.303%   $256.7498   $256.75   $256.75   $256.70  
  Purchase #5 $193.64   9.835%   $212.6845   $212.68   $212.70   $212.70  
  Purchase #6 $57.36   3.751%   $59.5116   $59.51   $59.50   $59.50  
  Purchase #7 $65.61   4.156%   $68.3368   $68.34   $68.35   $68.30  
  7 purchase totals = $979.20       $1,056.7834   $1,056.79   $1,056.80   $1,056.70