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 $243.85   10.682%   $269.8981   $269.90   $269.90   $269.90  
  Purchase #2 $24.88   3.168%   $25.6682   $25.67   $25.65   $25.70  
  Purchase #3 $46.45   6.608%   $49.5194   $49.52   $49.50   $49.50  
  Purchase #4 $37.83   8.698%   $41.1205   $41.12   $41.10   $41.10  
  Purchase #5 $196.93   12.690%   $221.9204   $221.92   $221.90   $221.90  
  Purchase #6 $233.50   5.264%   $245.7914   $245.79   $245.80   $245.80  
  Purchase #7 $220.74   5.512%   $232.9072   $232.91   $232.90   $232.90  
  7 purchase totals = $1,004.18       $1,086.8252   $1,086.83   $1,086.75   $1,086.80