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 $241.92   8.565%   $262.6404   $262.64   $262.65   $262.60  
  Purchase #2 $51.30   10.423%   $56.647   $56.65   $56.65   $56.60  
  Purchase #3 $203.26   4.565%   $212.5388   $212.54   $212.55   $212.50  
  Purchase #4 $88.55   10.166%   $97.552   $97.55   $97.55   $97.60  
  Purchase #5 $38.31   12.377%   $43.0516   $43.05   $43.05   $43.10  
  Purchase #6 $181.25   13.751%   $206.1737   $206.17   $206.15   $206.20  
  Purchase #7 $189.34   5.153%   $199.0967   $199.10   $199.10   $199.10  
  7 purchase totals = $993.93       $1,077.7002   $1,077.70   $1,077.70   $1,077.70