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 $61.39   13.814%   $69.8704   $69.87   $69.85   $69.90  
  Purchase #2 $165.73   7.112%   $177.5167   $177.52   $177.50   $177.50  
  Purchase #3 $160.73   11.111%   $178.5887   $178.59   $178.60   $178.60  
  Purchase #4 $121.31   10.366%   $133.885   $133.89   $133.90   $133.90  
  Purchase #5 $182.50   6.291%   $193.9811   $193.98   $194.00   $194.00  
  Purchase #6 $235.93   11.258%   $262.491   $262.49   $262.50   $262.50  
  Purchase #7 $124.80   11.268%   $138.8625   $138.86   $138.85   $138.90  
  7 purchase totals = $1,052.39       $1,155.1954   $1,155.20   $1,155.20   $1,155.30