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 $55.59   9.812%   $61.0445   $61.04   $61.05   $61.00  
  Purchase #2 $206.65   6.233%   $219.5305   $219.53   $219.55   $219.50  
  Purchase #3 $232.50   13.300%   $263.4225   $263.42   $263.40   $263.40  
  Purchase #4 $97.49   9.842%   $107.085   $107.09   $107.10   $107.10  
  Purchase #5 $35.59   9.442%   $38.9504   $38.95   $38.95   $39.00  
  Purchase #6 $173.40   6.104%   $183.9843   $183.98   $184.00   $184.00  
  Purchase #7 $129.92   12.760%   $146.4978   $146.50   $146.50   $146.50  
  7 purchase totals = $931.14       $1,020.5150   $1,020.51   $1,020.55   $1,020.50