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 $162.88   8.172%   $176.1906   $176.19   $176.20   $176.20  
  Purchase #2 $107.61   6.282%   $114.3701   $114.37   $114.35   $114.40  
  Purchase #3 $239.44   13.453%   $271.6519   $271.65   $271.65   $271.70  
  Purchase #4 $56.52   13.620%   $64.218   $64.22   $64.20   $64.20  
  Purchase #5 $199.94   7.122%   $214.1797   $214.18   $214.20   $214.20  
  Purchase #6 $51.69   8.495%   $56.0811   $56.08   $56.10   $56.10  
  Purchase #7 $126.91   8.813%   $138.0946   $138.09   $138.10   $138.10  
  7 purchase totals = $944.99       $1,034.7860   $1,034.78   $1,034.80   $1,034.90