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 $62.48   4.849%   $65.5097   $65.51   $65.50   $65.50  
  Purchase #2 $61.52   11.129%   $68.3666   $68.37   $68.35   $68.40  
  Purchase #3 $229.85   4.842%   $240.9793   $240.98   $241.00   $241.00  
  Purchase #4 $217.32   11.258%   $241.7859   $241.79   $241.80   $241.80  
  Purchase #5 $209.87   5.674%   $221.778   $221.78   $221.80   $221.80  
  Purchase #6 $136.98   12.870%   $154.6093   $154.61   $154.60   $154.60  
  Purchase #7 $27.26   12.397%   $30.6394   $30.64   $30.65   $30.60  
  7 purchase totals = $945.28       $1,023.6682   $1,023.68   $1,023.70   $1,023.70