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 $226.92   13.702%   $258.0126   $258.01   $258.00   $258.00  
  Purchase #2 $169.36   4.858%   $177.5875   $177.59   $177.60   $177.60  
  Purchase #3 $170.95   5.692%   $180.6805   $180.68   $180.70   $180.70  
  Purchase #4 $215.29   13.620%   $244.6125   $244.61   $244.60   $244.60  
  Purchase #5 $67.99   9.174%   $74.2274   $74.23   $74.25   $74.20  
  Purchase #6 $80.91   5.645%   $85.4774   $85.48   $85.50   $85.50  
  Purchase #7 $188.37   13.816%   $214.3952   $214.40   $214.40   $214.40  
  7 purchase totals = $1,119.79       $1,234.9931   $1,235.00   $1,235.05   $1,235.00