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 $94.31   4.299%   $98.3644   $98.36   $98.35   $98.40  
  Purchase #2 $190.26   9.368%   $208.0836   $208.08   $208.10   $208.10  
  Purchase #3 $218.36   4.869%   $228.9919   $228.99   $229.00   $229.00  
  Purchase #4 $50.80   4.293%   $52.9808   $52.98   $53.00   $53.00  
  Purchase #5 $243.80   5.694%   $257.682   $257.68   $257.70   $257.70  
  Purchase #6 $23.77   4.551%   $24.8518   $24.85   $24.85   $24.90  
  Purchase #7 $7.52   11.240%   $8.3652   $8.37   $8.35   $8.40  
  7 purchase totals = $828.82       $879.3197   $879.31   $879.35   $879.50