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 $49.62   12.368%   $55.757   $55.76   $55.75   $55.80  
  Purchase #2 $236.67   6.155%   $251.237   $251.24   $251.25   $251.20  
  Purchase #3 $207.76   12.135%   $232.9717   $232.97   $232.95   $233.00  
  Purchase #4 $88.42   8.107%   $95.5882   $95.59   $95.60   $95.60  
  Purchase #5 $172.94   4.820%   $181.2757   $181.28   $181.30   $181.30  
  Purchase #6 $19.34   9.516%   $21.1804   $21.18   $21.20   $21.20  
  Purchase #7 $38.48   10.228%   $42.4157   $42.42   $42.40   $42.40  
  7 purchase totals = $813.23       $880.4257   $880.44   $880.45   $880.50