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 $226.79   6.784%   $242.1754   $242.18   $242.20   $242.20  
  Purchase #2 $207.73   3.416%   $214.8261   $214.83   $214.85   $214.80  
  Purchase #3 $93.44   4.479%   $97.6252   $97.63   $97.65   $97.60  
  Purchase #4 $185.95   11.294%   $206.9512   $206.95   $206.95   $207.00  
  Purchase #5 $132.65   4.522%   $138.6484   $138.65   $138.65   $138.60  
  Purchase #6 $74.98   8.717%   $81.516   $81.52   $81.50   $81.50  
  Purchase #7 $45.91   8.560%   $49.8399   $49.84   $49.85   $49.80  
  7 purchase totals = $967.45       $1,031.5822   $1,031.60   $1,031.65   $1,031.50