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 $86.68   12.578%   $97.5826   $97.58   $97.60   $97.60  
  Purchase #2 $150.57   13.369%   $170.6997   $170.70   $170.70   $170.70  
  Purchase #3 $25.44   4.465%   $26.5759   $26.58   $26.60   $26.60  
  Purchase #4 $179.99   5.102%   $189.1731   $189.17   $189.15   $189.20  
  Purchase #5 $150.42   11.139%   $167.1753   $167.18   $167.20   $167.20  
  Purchase #6 $124.87   11.233%   $138.8966   $138.90   $138.90   $138.90  
  Purchase #7 $96.83   11.634%   $108.0952   $108.10   $108.10   $108.10  
  7 purchase totals = $814.80       $898.1984   $898.21   $898.25   $898.30