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 $196.62   6.758%   $209.9076   $209.91   $209.90   $209.90  
  Purchase #2 $41.69   4.397%   $43.5231   $43.52   $43.50   $43.50  
  Purchase #3 $167.43   5.423%   $176.5097   $176.51   $176.50   $176.50  
  Purchase #4 $216.86   8.404%   $235.0849   $235.08   $235.10   $235.10  
  Purchase #5 $191.71   3.592%   $198.5962   $198.60   $198.60   $198.60  
  Purchase #6 $62.97   7.350%   $67.5983   $67.60   $67.60   $67.60  
  Purchase #7 $54.96   5.713%   $58.0999   $58.10   $58.10   $58.10  
  7 purchase totals = $932.24       $989.3197   $989.32   $989.30   $989.30