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 $126.60   10.798%   $140.2703   $140.27   $140.25   $140.30  
  Purchase #2 $184.73   6.840%   $197.3655   $197.37   $197.35   $197.40  
  Purchase #3 $184.84   9.686%   $202.7436   $202.74   $202.75   $202.70  
  Purchase #4 $201.99   3.641%   $209.3445   $209.34   $209.35   $209.30  
  Purchase #5 $77.52   10.212%   $85.4363   $85.44   $85.45   $85.40  
  Purchase #6 $165.69   6.823%   $176.995   $177.00   $177.00   $177.00  
  Purchase #7 $220.61   3.357%   $228.0159   $228.02   $228.00   $228.00  
  7 purchase totals = $1,161.98       $1,240.1711   $1,240.18   $1,240.15   $1,240.10