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 $53.82   12.719%   $60.6654   $60.67   $60.65   $60.70  
  Purchase #2 $169.99   4.708%   $177.9931   $177.99   $178.00   $178.00  
  Purchase #3 $197.97   6.620%   $211.0756   $211.08   $211.10   $211.10  
  Purchase #4 $165.74   9.582%   $181.6212   $181.62   $181.60   $181.60  
  Purchase #5 $209.75   11.498%   $233.8671   $233.87   $233.85   $233.90  
  Purchase #6 $10.85   3.242%   $11.2018   $11.20   $11.20   $11.20  
  Purchase #7 $184.44   5.448%   $194.4883   $194.49   $194.50   $194.50  
  7 purchase totals = $992.56       $1,070.9125   $1,070.92   $1,070.90   $1,071.00