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 $24.30   10.375%   $26.8211   $26.82   $26.80   $26.80  
  Purchase #2 $235.48   3.247%   $243.126   $243.13   $243.15   $243.10  
  Purchase #3 $122.40   5.461%   $129.0843   $129.08   $129.10   $129.10  
  Purchase #4 $144.34   12.489%   $162.3666   $162.37   $162.35   $162.40  
  Purchase #5 $15.71   5.304%   $16.5433   $16.54   $16.55   $16.50  
  Purchase #6 $111.71   10.742%   $123.7099   $123.71   $123.70   $123.70  
  Purchase #7 $110.44   10.835%   $122.4062   $122.41   $122.40   $122.40  
  7 purchase totals = $764.38       $824.0574   $824.06   $824.05   $824.00