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 $211.42   10.152%   $232.8834   $232.88   $232.90   $232.90  
  Purchase #2 $243.64   9.666%   $267.1902   $267.19   $267.20   $267.20  
  Purchase #3 $63.32   7.215%   $67.8885   $67.89   $67.90   $67.90  
  Purchase #4 $91.72   9.662%   $100.582   $100.58   $100.60   $100.60  
  Purchase #5 $71.39   8.305%   $77.3189   $77.32   $77.30   $77.30  
  Purchase #6 $165.80   6.261%   $176.1807   $176.18   $176.20   $176.20  
  Purchase #7 $26.86   12.833%   $30.3069   $30.31   $30.30   $30.30  
  7 purchase totals = $874.15       $952.3506   $952.35   $952.40   $952.40