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 $68.98   6.746%   $73.6334   $73.63   $73.65   $73.60  
  Purchase #2 $239.25   7.714%   $257.7057   $257.71   $257.70   $257.70  
  Purchase #3 $208.56   11.215%   $231.95   $231.95   $231.95   $232.00  
  Purchase #4 $74.94   11.135%   $83.2846   $83.28   $83.30   $83.30  
  Purchase #5 $22.66   8.191%   $24.5161   $24.52   $24.50   $24.50  
  Purchase #6 $142.40   9.386%   $155.7657   $155.77   $155.75   $155.80  
  Purchase #7 $196.69   7.183%   $210.8182   $210.82   $210.80   $210.80  
  7 purchase totals = $953.48       $1,037.6737   $1,037.68   $1,037.65   $1,037.70