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 $114.94   7.873%   $123.9892   $123.99   $124.00   $124.00  
  Purchase #2 $196.49   8.392%   $212.9794   $212.98   $213.00   $213.00  
  Purchase #3 $145.65   7.240%   $156.1951   $156.20   $156.20   $156.20  
  Purchase #4 $132.54   11.303%   $147.521   $147.52   $147.50   $147.50  
  Purchase #5 $229.81   12.736%   $259.0786   $259.08   $259.10   $259.10  
  Purchase #6 $48.32   10.421%   $53.3554   $53.36   $53.35   $53.40  
  Purchase #7 $119.86   9.149%   $130.826   $130.83   $130.85   $130.80  
  7 purchase totals = $987.61       $1,083.9447   $1,083.96   $1,084.00   $1,084.00