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 $62.29   9.691%   $68.3265   $68.33   $68.35   $68.30  
  Purchase #2 $205.45   11.619%   $229.3212   $229.32   $229.30   $229.30  
  Purchase #3 $165.80   13.319%   $187.8829   $187.88   $187.90   $187.90  
  Purchase #4 $161.41   6.346%   $171.6531   $171.65   $171.65   $171.70  
  Purchase #5 $11.26   11.510%   $12.556   $12.56   $12.55   $12.60  
  Purchase #6 $26.68   3.819%   $27.6989   $27.70   $27.70   $27.70  
  Purchase #7 $181.76   11.745%   $203.1077   $203.11   $203.10   $203.10  
  7 purchase totals = $814.65       $900.5463   $900.55   $900.55   $900.60